[PATCH] Makefile: Unset stack-protector gcc flag if it is not supported

[Markos Chandras <markos.chandras@imgtec.com>]

In case the compiler does not support the stack-protector option,
unset the flag to avoid build failures. Printing a warning is enough
to let the user know that this flag will not be used.
Fixes the following build problem when using a toolchain which does
not support the -fstack-protector-strong flag:

Makefile:614: Cannot use CONFIG_CC_STACKPROTECTOR_STRONG:
-fstack-protector-strong not supported by compiler
mips-linux-gnu-gcc: error: unrecognized command line option
'-fstack-protector-strong'
scripts/Makefile.build:308: recipe for target 'scripts/mod/empty.o' failed
make[2]: *** [scripts/mod/empty.o] Error 1
make[2]: *** Waiting for unfinished jobs....
scripts/Makefile.build:455: recipe for target 'scripts/mod' failed

Cc: Michal Marek <mmarek@suse.cz>
Cc: linux-kbuild@vger.kernel.org
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
---
 Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Makefile b/Makefile
index 606ef7c..63a5333 100644
--- a/Makefile
+++ b/Makefile
@@ -607,12 +607,14 @@ ifdef CONFIG_CC_STACKPROTECTOR_REGULAR
   ifeq ($(call cc-option, $(stackp-flag)),)
     $(warning Cannot use CONFIG_CC_STACKPROTECTOR: \
 	      -fstack-protector not supported by compiler))
+    stackp-flag :=
   endif
 else ifdef CONFIG_CC_STACKPROTECTOR_STRONG
   stackp-flag := -fstack-protector-strong
   ifeq ($(call cc-option, $(stackp-flag)),)
     $(warning Cannot use CONFIG_CC_STACKPROTECTOR_STRONG: \
 	      -fstack-protector-strong not supported by compiler)
+    stackp-flag :=
   endif
 else
   # Force off for distro compilers that enable stack protector by default.
-- 
1.8.5.4