More fixes for systems that require -lm (re: 1afa007, 4edfa45)

As of 1afa007, the build fails on at least Arch and Kali Linux.

Analysis: same. The fix is just not complete yet. The -lm probe
programs in INIT (m*.c, compiled/linked via mkreq-maplib.sh in
INIT/Mamfile, but never run) are also written such that their
results are known at compile time, causing modern compilers to
optimise out the probe calls (on newer gcc, happens even with
-O0 (!)). This commit adds the same fix to them: rand() calls to
rule out optimisation.

Thanks to Marc Wilson (@posguy99) for the report.
Resolves: #716

src/cmd/INIT/m.c

@@ -2,7 +2,7 @@
 *                                                                      *
 *               This software is part of the ast package               *
 *          Copyright (c) 1994-2011 AT&T Intellectual Property          *
-*          Copyright (c) 2020-2023 Contributors to ksh 93u+m           *
+*          Copyright (c) 2020-2024 Contributors to ksh 93u+m           *
 *                      and is licensed under the                       *
 *                 Eclipse Public License, Version 2.0                  *
 *                                                                      *
@@ -17,16 +17,27 @@
 ***********************************************************************/
 /*
  * -lm test #1
+ *
+ * This program is compiled and linked by mkreq-maplib.sh via INIT/Mamfile
+ * but never actually run. It is only used to check if linking succeeds
+ * without or with -lm.
+ *
+ * For that test to work correctly, we must work around compiler optimization.
+ * The rand() call is to stop the result from being considered known at
+ * compile time, which would cause modern compilers to optimize out the probe
+ * calls, which would in turn cause linking to succeed where it shouldn't.
  */
 
-#ifndef sin
+#include <stdlib.h>
 #include <math.h>
-#endif
 
 int
 main(void)
 {
-	sin(0.0);
-	fmod(100.234, 11.0);
-	return 0;
+	double	f = (double)rand();
+	int	r = 0;
+
+	r |= sin(f) != 0.0;
+	r |= fmod(f, 11.0) != 0.0;
+	return r;
 }

src/cmd/INIT/m2.c

@@ -2,7 +2,7 @@
 *                                                                      *
 *               This software is part of the ast package               *
 *          Copyright (c) 1994-2011 AT&T Intellectual Property          *
-*          Copyright (c) 2020-2023 Contributors to ksh 93u+m           *
+*          Copyright (c) 2020-2024 Contributors to ksh 93u+m           *
 *                      and is licensed under the                       *
 *                 Eclipse Public License, Version 2.0                  *
 *                                                                      *
@@ -17,14 +17,24 @@
 ***********************************************************************/
 /*
  * -lm test #2
+ *
+ * This program is compiled and linked by mkreq-maplib.sh via INIT/Mamfile
+ * but never actually run. It is only used to check if linking succeeds
+ * without or with -lm.
+ *
+ * For that test to work correctly, we must work around compiler optimization.
+ * The rand() call is to stop the result from being considered known at
+ * compile time, which would cause modern compilers to optimize out the probe
+ * calls, which would in turn cause linking to succeed where it shouldn't.
  */
 
+#include <stdlib.h>
 #include <math.h>
 
 int
 main(void)
 {
-	double	value = 0;
+	double	value = (double)rand();
 	int	exp = 0;
 	int	r = 0;
 

src/cmd/INIT/m3.c

@@ -2,7 +2,7 @@
 *                                                                      *
 *               This software is part of the ast package               *
 *          Copyright (c) 1994-2011 AT&T Intellectual Property          *
-*          Copyright (c) 2020-2023 Contributors to ksh 93u+m           *
+*          Copyright (c) 2020-2024 Contributors to ksh 93u+m           *
 *                      and is licensed under the                       *
 *                 Eclipse Public License, Version 2.0                  *
 *                                                                      *
@@ -17,14 +17,24 @@
 ***********************************************************************/
 /*
  * -lm test #3
+ *
+ * This program is compiled and linked by mkreq-maplib.sh via INIT/Mamfile
+ * but never actually run. It is only used to check if linking succeeds
+ * without or with -lm.
+ *
+ * For that test to work correctly, we must work around compiler optimization.
+ * The rand() call is to stop the result from being considered known at
+ * compile time, which would cause modern compilers to optimize out the probe
+ * calls, which would in turn cause linking to succeed where it shouldn't.
  */
 
+#include <stdlib.h>
 #include <math.h>
 
 int
 main(void)
 {
-	long double	value = 0;
+	long double	value = (long double)rand();
 	int		exp = 0;
 	int		r = 0;
 

src/cmd/INIT/m4.c

@@ -2,7 +2,7 @@
 *                                                                      *
 *               This software is part of the ast package               *
 *          Copyright (c) 1994-2011 AT&T Intellectual Property          *
-*          Copyright (c) 2020-2023 Contributors to ksh 93u+m           *
+*          Copyright (c) 2020-2024 Contributors to ksh 93u+m           *
 *                      and is licensed under the                       *
 *                 Eclipse Public License, Version 2.0                  *
 *                                                                      *
@@ -17,14 +17,24 @@
 ***********************************************************************/
 /*
  * -lm test #4
+ *
+ * This program is compiled and linked by mkreq-maplib.sh via INIT/Mamfile
+ * but never actually run. It is only used to check if linking succeeds
+ * without or with -lm.
+ *
+ * For that test to work correctly, we must work around compiler optimization.
+ * The rand() call is to stop the result from being considered known at
+ * compile time, which would cause modern compilers to optimize out the probe
+ * calls, which would in turn cause linking to succeed where it shouldn't.
  */
 
+#include <stdlib.h>
 #include <math.h>
 
 int
 main(void)
 {
-	double	value = 0;
+	double	value = (double)rand();
 
 	return isnan(value);
 }

src/cmd/INIT/m5.c

@@ -2,7 +2,7 @@
 *                                                                      *
 *               This software is part of the ast package               *
 *          Copyright (c) 1994-2011 AT&T Intellectual Property          *
-*          Copyright (c) 2020-2023 Contributors to ksh 93u+m           *
+*          Copyright (c) 2020-2024 Contributors to ksh 93u+m           *
 *                      and is licensed under the                       *
 *                 Eclipse Public License, Version 2.0                  *
 *                                                                      *
@@ -17,14 +17,24 @@
 ***********************************************************************/
 /*
  * -lm test #5
+ *
+ * This program is compiled and linked by mkreq-maplib.sh via INIT/Mamfile
+ * but never actually run. It is only used to check if linking succeeds
+ * without or with -lm.
+ *
+ * For that test to work correctly, we must work around compiler optimization.
+ * The rand() call is to stop the result from being considered known at
+ * compile time, which would cause modern compilers to optimize out the probe
+ * calls, which would in turn cause linking to succeed where it shouldn't.
  */
 
+#include <stdlib.h>
 #include <math.h>
 
 int
 main(void)
 {
-	long double	value = 0;
+	long double	value = (long double)rand();
 
 	return isnanl(value);
 }

src/cmd/INIT/m6.c

@@ -2,7 +2,7 @@
 *                                                                      *
 *               This software is part of the ast package               *
 *          Copyright (c) 1994-2011 AT&T Intellectual Property          *
-*          Copyright (c) 2020-2023 Contributors to ksh 93u+m           *
+*          Copyright (c) 2020-2024 Contributors to ksh 93u+m           *
 *                      and is licensed under the                       *
 *                 Eclipse Public License, Version 2.0                  *
 *                                                                      *
@@ -17,16 +17,26 @@
 ***********************************************************************/
 /*
  * -lm test #6
+ *
+ * This program is compiled and linked by mkreq-maplib.sh via INIT/Mamfile
+ * but never actually run. It is only used to check if linking succeeds
+ * without or with -lm.
+ *
+ * For that test to work correctly, we must work around compiler optimization.
+ * The rand() call is to stop the result from being considered known at
+ * compile time, which would cause modern compilers to optimize out the probe
+ * calls, which would in turn cause linking to succeed where it shouldn't.
  */
 
 #define _ISOC99_SOURCE	1
 
+#include <stdlib.h>
 #include <math.h>
 
 int
 main(void)
 {
-	double	value = -0.0;
+	double	value = -((double)rand());
 
 	return !signbit(value);
 }