FROMLIST: BACKPORT: Makefile: lld: tell clang to use lld

This is needed because clang doesn't select which linker to use based on
$LD but rather -fuse-ld=lld. This is problematic especially for
cc-ldoption, which checks for linker flag support via invoking the
compiler, rather than the linker.

Link: ClangBuiltLinux/linux#342
Suggested-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Adam W. Willis <return.of.octobot@gmail.com>

Makefile

@@ -648,6 +648,12 @@ LDFINAL_vmlinux := $(LD)
 LD		:= $(LDLLD)
 endif
 
+ifeq ($(cc-name),clang)
+ifeq ($(ld-name),lld)
+KBUILD_CFLAGS	+= -fuse-ld=lld
+endif
+endif
+
 ifdef CONFIG_LTO_CLANG
 # use GNU gold with LLVMgold or LLD for LTO linking, and LD for vmlinux_link
 ifeq ($(ld-name),gold)