kbuild: introduce ccflags-y, asflags-y and ldflags-y

Introduce ccflags-y, asflags-y and ldflags-y so we soon can
deprecate use of EXTRA_CFLAGS, EXTRA_AFLAGS and EXTRA_LDFLAGS.
This patch does not touch any in-tree users - thats next round.
Lets get this committed first and then fix the users of the
soon to be deprecated variants next.

The rationale behind this change is to introduce support for
makefile fragments like:

ccflags-$(CONFIG_WHATEVER_DEBUG) := -DDEBUG

As a replacement for the uglier:
ifeq ($(CONFIG_WHATEVER_DEBUG),y)
        EXTRA_CFLAGS := -DDEBUG
endif

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

scripts/Makefile.lib

@@ -1,3 +1,9 @@
+# Backward compatibility
+asflags-y  += $(EXTRA_AFLAGS)
+ccflags-y  += $(EXTRA_CFLAGS)
+cppflags-y += $(EXTRA_CPPFLAGS)
+ldflags-y  += $(EXTRA_LDFLAGS)
+
 # Figure out what we need to build from the various variables
 # ===========================================================================
 
@@ -84,9 +90,9 @@ basename_flags = -D"KBUILD_BASENAME=KBUILD_STR($(call name-fix,$(basetarget)))"
 modname_flags  = $(if $(filter 1,$(words $(modname))),\
                  -D"KBUILD_MODNAME=KBUILD_STR($(call name-fix,$(modname)))")
 
-_c_flags       = $(KBUILD_CFLAGS) $(EXTRA_CFLAGS) $(CFLAGS_$(basetarget).o)
-_a_flags       = $(KBUILD_AFLAGS) $(EXTRA_AFLAGS) $(AFLAGS_$(basetarget).o)
-_cpp_flags     = $(KBUILD_CPPFLAGS) $(EXTRA_CPPFLAGS) $(CPPFLAGS_$(@F))
+_c_flags       = $(KBUILD_CFLAGS) $(ccflags-y) $(CFLAGS_$(basetarget).o)
+_a_flags       = $(KBUILD_AFLAGS) $(asflags-y) $(AFLAGS_$(basetarget).o)
+_cpp_flags     = $(KBUILD_CPPFLAGS) $(cppflags-y) $(CPPFLAGS_$(@F))
 
 # If building the kernel in a separate objtree expand all occurrences
 # of -Idir to -I$(srctree)/dir except for absolute paths (starting with '/').
@@ -115,7 +121,7 @@ a_flags        = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(KBUILD_CPPFLAGS) \
 
 cpp_flags      = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(__cpp_flags)
 
-ld_flags       = $(LDFLAGS) $(EXTRA_LDFLAGS)
+ld_flags       = $(LDFLAGS) $(ldflags-y)
 
 # Finds the multi-part object the current object will be linked into
 modname-multi = $(sort $(foreach m,$(multi-used),\
@@ -145,7 +151,7 @@ $(obj)/%:: $(src)/%_shipped
 # ---------------------------------------------------------------------------
 
 quiet_cmd_ld = LD      $@
-cmd_ld = $(LD) $(LDFLAGS) $(EXTRA_LDFLAGS) $(LDFLAGS_$(@F)) \
+cmd_ld = $(LD) $(LDFLAGS) $(ldflags-y) $(LDFLAGS_$(@F)) \
 	       $(filter-out FORCE,$^) -o $@ 
 
 # Objcopy