tools/nolibc: always disable stack protector for tests

Stack protectors need support from libc.
This support is not provided by nolibc which leads to compiler errors
when stack protectors are enabled by default in a compiler:

      CC      nolibc-test
    /usr/bin/ld: /tmp/ccqbHEPk.o: in function `stat':
    nolibc-test.c:(.text+0x1d1): undefined reference to `__stack_chk_fail'
    /usr/bin/ld: /tmp/ccqbHEPk.o: in function `poll.constprop.0':
    nolibc-test.c:(.text+0x37b): undefined reference to `__stack_chk_fail'
    /usr/bin/ld: /tmp/ccqbHEPk.o: in function `vfprintf.constprop.0':
    nolibc-test.c:(.text+0x712): undefined reference to `__stack_chk_fail'
    /usr/bin/ld: /tmp/ccqbHEPk.o: in function `pad_spc.constprop.0':
    nolibc-test.c:(.text+0x80d): undefined reference to `__stack_chk_fail'
    /usr/bin/ld: /tmp/ccqbHEPk.o: in function `printf':
    nolibc-test.c:(.text+0x8c4): undefined reference to `__stack_chk_fail'
    /usr/bin/ld: /tmp/ccqbHEPk.o:nolibc-test.c:(.text+0x12d4): more undefined references to `__stack_chk_fail' follow
    collect2: error: ld returned 1 exit status
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

tools/testing/selftests/nolibc/Makefile

 # SPDX-License-Identifier: GPL-2.0
 # Makefile for nolibc tests
 include ../../../scripts/Makefile.include
+# We need this for the "cc-option" macro.
+include ../../../build/Build.include
 
 # we're in ".../tools/testing/selftests/nolibc"
 ifeq ($(srctree),)
@@ -72,6 +74,7 @@ endif
 
 CFLAGS_s390 = -m64
 CFLAGS  ?= -Os -fno-ident -fno-asynchronous-unwind-tables $(CFLAGS_$(ARCH))
+CFLAGS  += $(call cc-option,-fno-stack-protector)
 LDFLAGS := -s
 
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