optimize.lunar: Ensure that flags are in the correct format

The daily builds everything with -Os for stage2, but -Os is a bad flag
for glibc, and -Os is either first or last in the CFLAGS, which makes
it so that bad_flags doesn't see it and doesn't remove it.

Therefore, put spaces before and after the contents of the various flags
variables so that bad_flags operates on them the right way.

libs/optimize.lunar

@@ -24,11 +24,13 @@ bad_flags()
         unset LDFLAGS
     else
         for BAD_FLAG in "$@" ; do
-            # XXX should probably figure whether these variables are
-            # guaranteed to start and end with spaces or not
+            CFLAGS=" $CFLAGS "
             CFLAGS="${CFLAGS// $BAD_FLAG / }"
+            CXXFLAGS=" $CXXFLAGS "
             CXXFLAGS="${CXXFLAGS// $BAD_FLAG / }"
+            CPPFLAGS=" $CPPFLAGS "
             CPPFLAGS="${CPPFLAGS// $BAD_FLAG / }"
+            LDFLAGS=" $LDFLAGS "
             LDFLAGS="${LDFLAGS// $BAD_FLAG / }"
         done
     fi