Fix stack-protector for powerpc

On powerpc, stack protector expects a function called
__stack_chk_fail_local() instead of __stack_chk_fail()

And some versions of GCC for powerpc default to TLS canary
instead of global canary, so always force GCC to use global
canary with -mstack-protector-guard=global

Cc: Joel Peshkin <joel.peshkin@broadcom.com>
Fixes: 4e9bce12432 ("Add support for stack-protector")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
diff --git a/Makefile b/Makefile
index ffeb722..1b347f4 100644
--- a/Makefile
+++ b/Makefile
@@ -750,6 +750,7 @@
 
 ifeq ($(CONFIG_STACKPROTECTOR),y)
 KBUILD_CFLAGS += $(call cc-option,-fstack-protector-strong)
+KBUILD_CFLAGS += $(call cc-option,-mstack-protector-guard=global)
 CFLAGS_EFI += $(call cc-option,-fno-stack-protector)
 else
 KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector)
diff --git a/common/stackprot.c b/common/stackprot.c
index d5b7061..6495951 100644
--- a/common/stackprot.c
+++ b/common/stackprot.c
@@ -18,3 +18,8 @@
 	panic("Stack smashing detected in function:\n%p relocated from %p",
 	      ra, ra - gd->reloc_off);
 }
+
+void __stack_chk_fail_local(void)
+{
+	__stack_chk_fail();
+}