[PATCH 3/4] kbuild: actually include Makefile.clang for clang builds

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Makefile.clang is included depending on CONFIG_CC_IS_CLANG, but its
location in the Makefile was before the config variables are included.

Instead of moving it farther down and risk it being included too late,
let's do as Linux does and consult CC_VERSION_TEXT instead of any
config variables.

Fixes: f41c4d7c5649 ("Makefile: add LLVM/clang support")
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
 Makefile | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index b5a7d0b9918b..a80e1b60d534 100644
--- a/Makefile
+++ b/Makefile
@@ -563,7 +563,13 @@ ifdef building_out_of_srctree
 	{ echo "# this is build directory, ignore it"; echo "*"; } > .gitignore
 endif
 
-ifeq ($(CONFIG_CC_IS_CLANG),y)
+# The expansion should be delayed until arch/$(SRCARCH)/Makefile is included.
+# Some architectures define CROSS_COMPILE in arch/$(SRCARCH)/Makefile.
+# CC_VERSION_TEXT is referenced from Kconfig (so it needs export),
+# and from include/config/auto.conf.cmd to detect the compiler upgrade.
+CC_VERSION_TEXT = $(subst $(pound),,$(shell LC_ALL=C $(CC) --version 2>/dev/null | head -n 1))
+
+ifneq ($(findstring clang,$(CC_VERSION_TEXT)),)
 include $(srctree)/scripts/Makefile.clang
 endif
 
@@ -578,7 +584,7 @@ include $(srctree)/scripts/Makefile.defconf
 # KBUILD_DEFCONFIG may point out an alternative default configuration
 # used for 'make defconfig'
 include $(srctree)/arch/$(SRCARCH)/Makefile
-export KBUILD_DEFCONFIG
+export KBUILD_DEFCONFIG CC_VERSION_TEXT
 
 config: outputmakefile scripts_basic FORCE
 	$(Q)$(MAKE) $(build)=scripts/kconfig $@
-- 
2.39.5