powerpc/vdso: Include CLANG_FLAGS explicitly in ldflags-y

[ Upstream commit a7e5eb53 ]

A future change will move CLANG_FLAGS from KBUILD_{A,C}FLAGS to
KBUILD_CPPFLAGS so that '--target' is available while preprocessing.
When that occurs, the following error appears when building the compat
PowerPC vDSO:

  clang: error: unsupported option '-mbig-endian' for target 'x86_64-pc-linux-gnu'
  make[3]: *** [.../arch/powerpc/kernel/vdso/Makefile:76: arch/powerpc/kernel/vdso/vdso32.so.dbg] Error 1

Explicitly add CLANG_FLAGS to ldflags-y, so that '--target' will always
be present.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Stable-dep-of: d677ce52 ("powerpc/vdso: Drop -mstack-protector-guard flags in 32-bit files with clang")
Signed-off-by: Sasha Levin <sashal@kernel.org>