The $(CPP) (do only preprocessing) macro is already defined in Makefile.
However POWERPC redefines it and adds $(KBUILD_CFLAGS) which results
in flags duplication. Which is not a big deal by itself except for
the flags which depend on other flags and the compiler checks them
as it parses the command line.

Specifically, scripts/Makefile.build:304 generates ksyms for .S files.
If clang+llvm+sanitizer are enabled, this results in

-emit-llvm-bc -fno-lto -flto -fvisibility=hidden \
  -fsanitize=cfi-mfcall -fno-lto  ...

in the clang command line and triggers error:

clang-13: error: invalid argument '-fsanitize=cfi-mfcall' only allowed with '-flto'

This removes unnecessary CPP redefinition. Which works fine as in most
place KBUILD_CFLAGS is passed to $CPP except
arch/powerpc/kernel/vdso64/vdso(32|64).lds (and probably some others,
not yet detected). To fix vdso, we do:
1. explicitly add -m(big|little)-endian to $CPP
2. (for clang) add $CLANG_FLAGS to $KBUILD_CPPFLAGS as otherwise clang
silently ignores -m(big|little)-endian if the building platform does not
support big endian (such as x86) so --prefix= is required.

While at this, remove some duplication from CPPFLAGS_vdso(32|64)
as cmd_cpp_lds_S has them anyway. It still puzzles me why we need -C
(preserve comments in the preprocessor output) flag here.

Signed-off-by: Alexey Kardashevskiy <redacted>
---
Changes:
v2:
* fix KBUILD_CPPFLAGS
* add CLANG_FLAGS to CPPFLAGS
---
  Makefile                            | 1 +
  arch/powerpc/Makefile               | 3 ++-
  arch/powerpc/kernel/vdso32/Makefile | 2 +-
  arch/powerpc/kernel/vdso64/Makefile | 2 +-
  4 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/Makefile b/Makefile
index 72af8e423f11..13acd2183d55 100644
--- a/Makefile
+++ b/Makefile

@@ -591,6 +591,7 @@ CLANG_FLAGS	+= --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
  endif
  CLANG_FLAGS	+= -Werror=unknown-warning-option
  KBUILD_CFLAGS	+= $(CLANG_FLAGS)
+KBUILD_CPPFLAGS	+= $(CLANG_FLAGS)

  KBUILD_AFLAGS	+= $(CLANG_FLAGS)
  export CLANG_FLAGS
  endif

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 3212d076ac6a..306bfd2797ad 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile

@@ -76,6 +76,7 @@ endif
  
  ifdef CONFIG_CPU_LITTLE_ENDIAN
  KBUILD_CFLAGS	+= -mlittle-endian
+KBUILD_CPPFLAGS	+= -mlittle-endian
  KBUILD_LDFLAGS	+= -EL
  LDEMULATION	:= lppc
  GNUTARGET	:= powerpcle

@@ -83,6 +84,7 @@ MULTIPLEWORD	:= -mno-multiple
  KBUILD_CFLAGS_MODULE += $(call cc-option,-mno-save-toc-indirect)
  else
  KBUILD_CFLAGS += $(call cc-option,-mbig-endian)
+KBUILD_CPPFLAGS += $(call cc-option,-mbig-endian)
  KBUILD_LDFLAGS	+= -EB
  LDEMULATION	:= ppc
  GNUTARGET	:= powerpc

@@ -208,7 +210,6 @@ KBUILD_CPPFLAGS	+= -I $(srctree)/arch/$(ARCH) $(asinstr)
  KBUILD_AFLAGS	+= $(AFLAGS-y)
  KBUILD_CFLAGS	+= $(call cc-option,-msoft-float)
  KBUILD_CFLAGS	+= -pipe $(CFLAGS-y)
-CPP		= $(CC) -E $(KBUILD_CFLAGS)
  
  CHECKFLAGS	+= -m$(BITS) -D__powerpc__ -D__powerpc$(BITS)__
  ifdef CONFIG_CPU_BIG_ENDIAN

diff --git a/arch/powerpc/kernel/vdso32/Makefile b/arch/powerpc/kernel/vdso32/Makefile
index 7d9a6fee0e3d..ea001c6df1fa 100644
--- a/arch/powerpc/kernel/vdso32/Makefile
+++ b/arch/powerpc/kernel/vdso32/Makefile

@@ -44,7 +44,7 @@ asflags-y := -D__VDSO32__ -s
  
  obj-y += vdso32_wrapper.o
  targets += vdso32.lds
-CPPFLAGS_vdso32.lds += -P -C -Upowerpc
+CPPFLAGS_vdso32.lds += -C
  
  # link rule for the .so file, .lds has to be first
  $(obj)/vdso32.so.dbg: $(src)/vdso32.lds $(obj-vdso32) $(obj)/vgettimeofday.o FORCE

diff --git a/arch/powerpc/kernel/vdso64/Makefile b/arch/powerpc/kernel/vdso64/Makefile
index 2813e3f98db6..07eadba48c7a 100644
--- a/arch/powerpc/kernel/vdso64/Makefile
+++ b/arch/powerpc/kernel/vdso64/Makefile

@@ -30,7 +30,7 @@ ccflags-y := -shared -fno-common -fno-builtin -nostdlib \
  asflags-y := -D__VDSO64__ -s
  
  targets += vdso64.lds
-CPPFLAGS_vdso64.lds += -P -C -U$(ARCH)
+CPPFLAGS_vdso64.lds += -C
  
  # link rule for the .so file, .lds has to be first
  $(obj)/vdso64.so.dbg: $(src)/vdso64.lds $(obj-vdso64) $(obj)/vgettimeofday.o FORCE