command -x: fix bypassing path-bound built-ins again (re: be79e4e)

Symptom, after compiling ksh with support for dynamic libraries
(this will again become possible soon, we're currently testing it),
if the virtual /opt/ast/bin directory for path-bound built-ins is
first in $PATH:

   $ ksh -c 'command -vx cat; command -vx cat'
   /opt/ast/bin/cat
   /bin/cat

This already showed up in a regression test failure for the
dynamically linked ksh:

   path.sh[1008]: FAIL: 'command -vx' breakage (expected status 0,
   /bin/cat; got status 0, /opt/ast/bin/cat)

src/cmd/ksh93/sh/path.c: path_absolute():
- Add missing check for SH_XARG shell state bit.

src/cmd/ksh93/sh/path.c

@@ -800,7 +800,7 @@ Pathcomp_t *path_absolute(const char *name, Pathcomp_t *pp, int flag)
 					np->nvenv = dll;
 					goto found;
 				}
-				if(*stkptr(sh.stk,PATH_OFFSET)=='/' && nv_search(stkptr(sh.stk,PATH_OFFSET),sh.bltin_tree,0))
+				if(!sh_isstate(SH_XARG) && *stkptr(sh.stk,PATH_OFFSET)=='/' && nv_search(stkptr(sh.stk,PATH_OFFSET),sh.bltin_tree,0))
 					goto found;
 				if(fp)
 					free(fp);