x86/build: Fix build with older GCC versions

Older GCC (observed with 4.1.x) doesn't support -Wno-override-init and
also doesn't ignore unknown -Wno-* options.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Cc: Valdis.Kletnieks@vt.edu
Fixes: 5e44258d16 "x86/build: Reduce the W=1 warnings noise when compiling x86 syscall tables"
Link: http://lkml.kernel.org/r/580E3E1C02000078001191C4@prv-mh.provo.novell.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/entry/Makefile

@@ -5,8 +5,8 @@
 OBJECT_FILES_NON_STANDARD_entry_$(BITS).o   := y
 OBJECT_FILES_NON_STANDARD_entry_64_compat.o := y
 
-CFLAGS_syscall_64.o		+= -Wno-override-init
-CFLAGS_syscall_32.o		+= -Wno-override-init
+CFLAGS_syscall_64.o		+= $(call cc-option,-Wno-override-init,)
+CFLAGS_syscall_32.o		+= $(call cc-option,-Wno-override-init,)
 obj-y				:= entry_$(BITS).o thunk_$(BITS).o syscall_$(BITS).o
 obj-y				+= common.o