[PATCH] stdlib: tests: don't double-define _FORTIFY_SOURCE

[Sam James]

If using -D_FORITFY_SOURCE=3 (in my case, I've patched GCC to add
=3 instead of =2 (we've done =2 for years in Gentoo)), building
glibc tests will fail on testmb like:
```
<command-line>: error: "_FORTIFY_SOURCE" redefined [-Werror]
<built-in>: note: this is the location of the previous definition
cc1: all warnings being treated as errors
make[2]: *** [../o-iterator.mk:9: /var/tmp/portage/sys-libs/glibc-2.36/work/build-x86-x86_64-pc-linux-gnu-nptl/stdlib/testmb.o] Error 1
make[2]: *** Waiting for unfinished jobs....
```

It's just because we're always setting -D_FORTIFY_SOURCE=2
rather than unsetting it first. If F_S is already 2, it's harmless,
but if it's another value (say, 1, or 3), the compiler will bawk.

(I'm not aware of a reason this couldn't be tested with =3,
but the toolchain support is limited for that (too new), and we want
to run the tests everywhere possible.)

Signed-off-by: Sam James <sam@gentoo.org>
---
 stdlib/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/stdlib/Makefile b/stdlib/Makefile
index f7b25c1981..d8b59022cc 100644
--- a/stdlib/Makefile
+++ b/stdlib/Makefile
@@ -380,7 +380,7 @@ CFLAGS-tst-qsort.c += $(stack-align-test-flags)
 CFLAGS-tst-makecontext.c += -funwind-tables
 CFLAGS-tst-makecontext2.c += $(stack-align-test-flags)
 
-CFLAGS-testmb.c += -D_FORTIFY_SOURCE=2 -Wall -Werror
+CFLAGS-testmb.c += -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -Wall -Werror
 
 
 # Run a test on the header files we use.
-- 
2.37.1