kbuild: Use -nostdinc with kernel sources

Kernel code should not include userspace headers. To avoid that
happening by mistake, ask gcc not to look into the usual places
when looking for headers. We still need to find gcc headers for
vararg and similar, though - achieved by the "-iwithprefix include"
which will look into <gcc-path>/include, as proposed by Russell
King.

A similar patch went into 2.4, so not much breakage expected.

Makefile

@@ -110,12 +110,13 @@ AFLAGS_MODULE   = $(MODFLAGS)
 CFLAGS_KERNEL	=
 AFLAGS_KERNEL	=
 EXPORT_FLAGS    =
+NOSTDINC_FLAGS  = -nostdinc -iwithprefix include
 
 export	VERSION PATCHLEVEL SUBLEVEL EXTRAVERSION KERNELRELEASE ARCH \
 	CONFIG_SHELL TOPDIR HPATH HOSTCC HOSTCFLAGS CROSS_COMPILE AS LD CC \
 	CPP AR NM STRIP OBJCOPY OBJDUMP MAKE MAKEFILES GENKSYMS PERL
 
-export CPPFLAGS EXPORT_FLAGS
+export CPPFLAGS EXPORT_FLAGS NOSTDINC_FLAGS
 export CFLAGS CFLAGS_KERNEL CFLAGS_MODULE 
 export AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
 

Rules.make

@@ -121,7 +121,7 @@ $(export-objs:.o=.i)  : export_flags   := $(EXPORT_FLAGS)
 $(export-objs:.o=.s)  : export_flags   := $(EXPORT_FLAGS)
 $(export-objs:.o=.lst): export_flags   := $(EXPORT_FLAGS)
 
-c_flags = $(CFLAGS) $(modkern_cflags) $(EXTRA_CFLAGS) $(CFLAGS_$(*F).o) -DKBUILD_BASENAME=$(subst $(comma),_,$(subst -,_,$(*F))) $(export_flags)
+c_flags = $(CFLAGS) $(NOSTDINC_FLAGS) $(modkern_cflags) $(EXTRA_CFLAGS) $(CFLAGS_$(*F).o) -DKBUILD_BASENAME=$(subst $(comma),_,$(subst -,_,$(*F))) $(export_flags) 
 
 quiet_cmd_cc_s_c = CC     $(RELDIR)/$@
 cmd_cc_s_c       = $(CC) $(c_flags) -S -o $@ $< 
@@ -159,7 +159,7 @@ $(real-objs-y:.o=.s): modkern_aflags := $(AFLAGS_KERNEL)
 $(real-objs-m)      : modkern_aflags := $(AFLAGS_MODULE)
 $(real-objs-m:.o=.s): modkern_aflags := $(AFLAGS_MODULE)
 
-a_flags = $(AFLAGS) $(modkern_aflags) $(EXTRA_AFLAGS) $(AFLAGS_$(*F).o)
+a_flags = $(AFLAGS) $(NOSTDINC_FLAGS) $(modkern_aflags) $(EXTRA_AFLAGS) $(AFLAGS_$(*F).o)
 
 quiet_cmd_as_s_S = CPP    $(RELDIR)/$@
 cmd_as_s_S       = $(CPP) $(a_flags)   -o $@ $<