kbuild: enable 'make AFLAGS=...' to add additional options to AS

The variable AFLAGS is a wellknown variable and the usage by
kbuild may result in unexpected behaviour.
On top of that several people over time has asked for a way to
pass in additional flags to gcc.

This patch replace use of AFLAGS with KBUILD_AFLAGS all over
the tree.

Patch was tested on following architectures:
alpha, arm, i386, x86_64, mips, sparc, sparc64, ia64, m68k, s390

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
diff --git a/arch/um/sys-ppc/Makefile b/arch/um/sys-ppc/Makefile
index af20026..a9814a7 100644
--- a/arch/um/sys-ppc/Makefile
+++ b/arch/um/sys-ppc/Makefile
@@ -1,7 +1,7 @@
 OBJ = built-in.o
 
 .S.o:
-	$(CC) $(AFLAGS) -D__ASSEMBLY__ -D__UM_PPC__ -c $< -o $*.o
+	$(CC) $(KBUILD_AFLAGS) -D__ASSEMBLY__ -D__UM_PPC__ -c $< -o $*.o
 
 OBJS = ptrace.o sigcontext.o semaphore.o checksum.o miscthings.o misc.o \
 	ptrace_user.o sysrq.o
@@ -57,13 +57,13 @@
 checksum.o: checksum.S
 	rm -f asm
 	ln -s $(TOPDIR)/include/asm-ppc asm
-	$(CC) $(EXTRA_AFLAGS) $(AFLAGS) -D__ASSEMBLY__ -D__UM_PPC__ -c $< -o $*.o
+	$(CC) $(EXTRA_AFLAGS) $(KBUILD_AFLAGS) -D__ASSEMBLY__ -D__UM_PPC__ -c $< -o $*.o
 	rm -f asm
 
 misc.o: misc.S ppc_defs.h
 	rm -f asm
 	ln -s $(TOPDIR)/include/asm-ppc asm
-	$(CC) $(EXTRA_AFLAGS) $(AFLAGS) -D__ASSEMBLY__ -D__UM_PPC__ -c $< -o $*.o
+	$(CC) $(EXTRA_AFLAGS) $(KBUILD_AFLAGS) -D__ASSEMBLY__ -D__UM_PPC__ -c $< -o $*.o
 	rm -f asm
 
 clean-files := $(OBJS) ppc_defs.h checksum.S semaphore.c mk_defs.c