powerpc/boot: Set target when cross-compiling for clang

commit 813af51f5d30a2da6a2523c08465f9726e51772e upstream.

Clang needs to be told which target it is building for when cross
compiling.

Link: ClangBuiltLinux/linux#259
Signed-off-by: Joel Stanley <joel@jms.id.au>
Tested-by: Daniel Axtens <dja@axtens.net> # powerpc 64-bit BE
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
[nc: Use 'ifeq ($(cc-name),clang)' instead of 'ifdef CONFIG_CC_IS_CLANG'
     because that config does not exist in 4.14; the Kconfig rewrite
     that added that config happened in 4.18]
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/powerpc/boot/Makefile

@@ -49,6 +49,11 @@ endif
 
 BOOTAFLAGS	:= -D__ASSEMBLY__ $(BOOTCFLAGS) -traditional -nostdinc
 
+ifeq ($(cc-name),clang)
+BOOTCFLAGS += $(CLANG_FLAGS)
+BOOTAFLAGS += $(CLANG_FLAGS)
+endif
+
 ifdef CONFIG_DEBUG_INFO
 BOOTCFLAGS	+= -g
 endif