They may contain all kinds of things that make the test fail.
See #2823 for details
SAVE_CFLAGS="$CFLAGS"
CFLAGS="-Wall -Werror"
SAVE_CFLAGS="$CFLAGS"
CFLAGS="-Wall -Werror"
+SAVE_LDFAGS="$LDFLAGS"
+LDFLAGS=""
AC_CACHE_CHECK([for strtok_r],
[c_cv_have_strtok_r_default],
AC_CACHE_CHECK([for strtok_r],
[c_cv_have_strtok_r_default],
if test "x$c_cv_have_strtok_r_reentrant" = "xyes"; then
CFLAGS="$CFLAGS -D_REENTRANT=1"
fi
if test "x$c_cv_have_strtok_r_reentrant" = "xyes"; then
CFLAGS="$CFLAGS -D_REENTRANT=1"
fi