The kernel uses `-include` to include include/linux/compiler_types.h
into all translation units (see scripts/Makefile.lib), which #includes
compiler_attributes.h.

arch/powerpc/boot/ uses different compiler flags from the rest of the
kernel. As such, it doesn't contain the definitions from these headers,
and redefines a few that it needs.

For the purpose of enabling -Wimplicit-fallthrough for ppc, include
compiler_attributes.h via `-include`.

It was also noted in 6a9dc5fd6170 that we could -D__KERNEL__ and
-include compiler_types.h like the main kernel does, though testing that
produces a whole sea of warnings to cleanup. This approach is minimally
invasive.

Signed-off-by: Nick Desaulniers <redacted>
Tested-by: Nathan Chancellor <redacted>
Reviewed-by: Nathan Chancellor <redacted>
Acked-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://github.com/ClangBuiltLinux/linux/issues/236
---
 arch/powerpc/boot/Makefile     | 1 +
 arch/powerpc/boot/decompress.c | 1 -
 2 files changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/boot/Makefile b/arch/powerpc/boot/Makefile
index f8ce6d2dde7b..1659963a8f1d 100644
--- a/arch/powerpc/boot/Makefile
+++ b/arch/powerpc/boot/Makefile

@@ -31,6 +31,7 @@ endif
 BOOTCFLAGS    := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
 		 -fno-strict-aliasing -O2 -msoft-float -mno-altivec -mno-vsx \
 		 -pipe -fomit-frame-pointer -fno-builtin -fPIC -nostdinc \
+		 -include $(srctree)/include/linux/compiler_attributes.h \
 		 $(LINUXINCLUDE)
 
 ifdef CONFIG_PPC64_BOOT_WRAPPER

diff --git a/arch/powerpc/boot/decompress.c b/arch/powerpc/boot/decompress.c
index 8bf39ef7d2df..6098b879ac97 100644
--- a/arch/powerpc/boot/decompress.c
+++ b/arch/powerpc/boot/decompress.c

@@ -21,7 +21,6 @@
 
 #define STATIC static
 #define INIT
-#define __always_inline inline
 
 /*
  * The build process will copy the required zlib source files and headers

-- 
2.29.2.299.gdc1121823c-goog