x86, boot: Restrict CFLAGS for hostprogs

Currently tools/build has access to all the kernel headers in
$(srctree). This is unnecessary and could potentially allow
tools/build to erroneously include kernel headers when it should only
be including userspace-exported headers.

Unfortunately, mkcpustr still needs access to some of the asm kernel
headers, so explicitly special case that hostprog.

Cc: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
Link: http://lkml.kernel.org/r/1330436245-24875-5-git-send-email-matt@console-pimps.org
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/boot/Makefile

@@ -37,8 +37,9 @@ setup-y		+= video-bios.o
 targets		+= $(setup-y)
 hostprogs-y	:= mkcpustr tools/build
 
-HOST_EXTRACFLAGS += $(LINUXINCLUDE)
-
+HOSTCFLAGS_mkcpustr.o := -I$(srctree)/arch/$(SRCARCH)/include
+HOST_EXTRACFLAGS += -I$(objtree)/include -I$(srctree)/tools/include \
+                   -include $(srctree)/include/linux/kconfig.h
 $(obj)/cpu.o: $(obj)/cpustr.h
 
 quiet_cmd_cpustr = CPUSTR  $@