FROMLIST: BACKPORT: Makefile: clang: choose GCC_TOOLCHAIN_DIR not on LD

This causes an issue when trying to build with `make LD=ld.lld` if
ld.lld and the rest of your cross tools aren't in the same directory
(ex. /usr/local/bin) (as is the case for Android's build system), as the
GCC_TOOLCHAIN_DIR then gets set based on `which $(LD)` which will point
where LLVM tools are, not GCC/binutils tools are located.

Instead, select the GCC_TOOLCHAIN_DIR based on another tool provided by
binutils for which LLVM does not provide a substitute for, such as
elfedit.

Fixes commit 785f11aa595b ("kbuild: Add better clang cross build support")

Link: ClangBuiltLinux/linux#341
Suggested-by: Nathan Chancellor <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
Tested-by: Nathan Chancellor <[email protected]>
Signed-off-by: Nick Desaulniers <[email protected]>

Makefile

@@ -516,7 +516,7 @@ CLANG_TARGET	:= --target=$(notdir $(CLANG_TRIPLE:%-=%))
 ifeq ($(shell $(srctree)/scripts/clang-android.sh $(CC) $(CLANG_TARGET)), y)
 $(error "Clang with Android --target detected. Did you specify CLANG_TRIPLE?")
 endif
-GCC_TOOLCHAIN_DIR := $(dir $(shell which $(LD)))
+GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
 CLANG_PREFIX	:= --prefix=$(GCC_TOOLCHAIN_DIR)
 GCC_TOOLCHAIN	:= $(realpath $(GCC_TOOLCHAIN_DIR)/..)
 endif