BACKPORT: arm64: vdso32: suppress error message for 'make mrproper'

commit 14831fad73f5ac30ac61760487d95a538e6ab3cb upstream.

When running the following command without arm-linux-gnueabi-gcc in
one's $PATH, the following warning is observed:

$ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make -j72 LLVM=1 mrproper
make[1]: arm-linux-gnueabi-gcc: No such file or directory

This is because KCONFIG is not run for mrproper, so CONFIG_CC_IS_CLANG
is not set, and we end up eagerly evaluating various variables that try
to invoke CC_COMPAT.

This is a similar problem to what was observed in
commit dc960bfeedb0 ("h8300: suppress error messages for 'make clean'")

Reported-by: Lucas Henneman <[email protected]>
Suggested-by: Masahiro Yamada <[email protected]>
[nd: adjusted context due to missing e35123d83ee3]
[nd: backported because Android backported compat vdso support to 4.19.y]
Signed-off-by: Nick Desaulniers <[email protected]>
Reviewed-by: Vincenzo Frascino <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
Tested-by: Nathan Chancellor <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>
Bug: 202827173
Change-Id: Ic1ad9eb2871fd4f6c4f0e27df673df5cb4012df9
Signed-off-by: engstk <[email protected]>

Author: nickdesaulniers

arch/arm64/kernel/vdso32/Makefile

@@ -40,7 +40,8 @@ cc32-as-instr = $(call try-run,\
 # As a result we set our own flags here.
 
 # KBUILD_CPPFLAGS and NOSTDINC_FLAGS from top-level Makefile
-VDSO_CPPFLAGS := -D__KERNEL__ -nostdinc -isystem $(shell $(CC_COMPAT) -print-file-name=include)
+VDSO_CPPFLAGS := -D__KERNEL__ -nostdinc
+VDSO_CPPFLAGS += -isystem $(shell $(CC_COMPAT) -print-file-name=include 2>/dev/null)
 VDSO_CPPFLAGS += $(LINUXINCLUDE)
 
 # Common C and assembly flags