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 <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Valdis Kletnieks <[e-mail]>
Cc: [e-mail]
Fixes: 5e44258d16 "x86/build: Reduce the W=1 warnings noise when compiling x86 syscall tables"
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/entry/Makefile

···
 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