BACKPORT: Makefile: move initial clang flag handling into scripts/Makefile.clang

With some of the changes we'd like to make to CROSS_COMPILE, the initial
block of clang flag handling which controls things like the target triple,
whether or not to use the integrated assembler and how to find GAS,
and erroring on unknown warnings is becoming unwieldy. Move it into its
own file under scripts/.

Reviewed-by: Nathan Chancellor <[email protected]>
Signed-off-by: Nick Desaulniers <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>
Bug: 209655537
[nd: conflict in MAINTAINERS]
(cherry picked from commit 6f5b41a2f5a6314614e286274eb8e985248aac60)
Change-Id: I350ba8aaf924f7b373d25ef67260e6373a405d12

Author: nickdesaulniers

MAINTAINERS

@@ -4032,6 +4032,8 @@ C:	irc://chat.freenode.net/clangbuiltlinux
 S:	Supported
 K:	\b(?i:clang|llvm)\b
 F:	Documentation/kbuild/llvm.rst
+F:	include/linux/compiler-clang.h
+F:	scripts/Makefile.clang
 
 CLEANCACHE API
 M:	Konrad Rzeszutek Wilk <[email protected]>

Makefile

@@ -561,18 +561,7 @@ endif
 CC_VERSION_TEXT = $(subst $(pound),,$(shell LC_ALL=C $(CC) --version 2>/dev/null | head -n 1))
 
 ifneq ($(findstring clang,$(CC_VERSION_TEXT)),)
-ifneq ($(CROSS_COMPILE),)
-CLANG_FLAGS	+= --target=$(notdir $(CROSS_COMPILE:%-=%))
-endif
-ifneq ($(LLVM_IAS),1)
-CLANG_FLAGS	+= -no-integrated-as
-GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
-CLANG_FLAGS	+= --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
-endif
-CLANG_FLAGS	+= -Werror=unknown-warning-option
-KBUILD_CFLAGS	+= $(CLANG_FLAGS)
-KBUILD_AFLAGS	+= $(CLANG_FLAGS)
-export CLANG_FLAGS
+include $(srctree)/scripts/Makefile.clang
 endif
 
 # Include this also for config targets because some architectures need

scripts/Makefile.clang

@@ -0,0 +1,14 @@
+ifneq ($(CROSS_COMPILE),)
+CLANG_FLAGS	+= --target=$(notdir $(CROSS_COMPILE:%-=%))
+endif
+ifeq ($(LLVM_IAS),1)
+CLANG_FLAGS	+= -integrated-as
+else
+CLANG_FLAGS	+= -no-integrated-as
+GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
+CLANG_FLAGS	+= --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
+endif
+CLANG_FLAGS	+= -Werror=unknown-warning-option
+KBUILD_CFLAGS	+= $(CLANG_FLAGS)
+KBUILD_AFLAGS	+= $(CLANG_FLAGS)
+export CLANG_FLAGS