kbuild: make cc-version available in kbuild files

Move $(CC) support functions to Kbuild.include so they are available
in the kbuild files.
In addition the following was done:
	o as-option documented in Documentation/kbuild/makefiles.txt
	o Moved documentation to new section to match
	  new scope of functions
	o added cc-ifversion used to conditionally select a text string
	  dependent on actual $(CC) version
	o documented cc-ifversion
	o change so Kbuild.include is read before the kbuild file

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

scripts/Kbuild.include

@@ -44,6 +44,43 @@ define filechk
 	fi
 endef
 
+######
+# cc support functions to be used (only) in arch/$(ARCH)/Makefile
+# See documentation in Documentation/kbuild/makefiles.txt
+
+# as-option
+# Usage: cflags-y += $(call as-option, -Wa$(comma)-isa=foo,)
+
+as-option = $(shell if $(CC) $(CFLAGS) $(1) -Wa,-Z -c -o /dev/null \
+	     -xassembler /dev/null > /dev/null 2>&1; then echo "$(1)"; \
+	     else echo "$(2)"; fi ;)
+
+# cc-option
+# Usage: cflags-y += $(call cc-option, -march=winchip-c6, -march=i586)
+
+cc-option = $(shell if $(CC) $(CFLAGS) $(1) -S -o /dev/null -xc /dev/null \
+             > /dev/null 2>&1; then echo "$(1)"; else echo "$(2)"; fi ;)
+
+# cc-option-yn
+# Usage: flag := $(call cc-option-yn, -march=winchip-c6)
+cc-option-yn = $(shell if $(CC) $(CFLAGS) $(1) -S -o /dev/null -xc /dev/null \
+                > /dev/null 2>&1; then echo "y"; else echo "n"; fi;)
+
+# cc-option-align
+# Prefix align with either -falign or -malign
+cc-option-align = $(subst -functions=0,,\
+	$(call cc-option,-falign-functions=0,-malign-functions=0))
+
+# cc-version
+# Usage gcc-ver := $(call cc-version, $(CC))
+cc-version = $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-version.sh \
+              $(if $(1), $(1), $(CC)))
+
+# cc-ifversion
+# Usage:  EXTRA_CFLAGS += $(call cc-ifversion, -lt, 0402, -O1)
+cc-ifversion = $(shell if [ $(call cc-version, $(CC)) $(1) $(2) ]; then \
+                       echo $(3); fi;)
+
 ###
 # Shorthand for $(Q)$(MAKE) -f scripts/Makefile.build obj=
 # Usage: