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

[Siddhesh Poyarekar <siddhesh@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=35bcb08eaa953c9b8bef6ab2486dc4361e1f26c0

commit 35bcb08eaa953c9b8bef6ab2486dc4361e1f26c0
Author: Sam James <sam@gentoo.org>
Date:   Thu Feb 2 23:00:31 2023 -0500

    stdlib: tests: don't double-define _FORTIFY_SOURCE
    
    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>
    Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

Diff:
---
 stdlib/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/stdlib/Makefile b/stdlib/Makefile
index e0fc82fc4d..83391d00c1 100644
--- a/stdlib/Makefile
+++ b/stdlib/Makefile
@@ -392,7 +392,7 @@ 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.