BACKPORT: arm64: vdso32: Enable Clang Compilation

Enable Clang Compilation for the vdso32 library.

Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Nathan Chancellor <natechancellor@gmail.com> # build
Tested-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lkml.kernel.org/r/20200320145351.32292-27-vincenzo.frascino@arm.com


(cherry picked from commit a5d442f50a41d7c5a6a97b19c49d8a1ee0cf128b)
Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 154668398
Change-Id: Ib9d9fa06b69797a8ecc6d0fdce4b0b02e71b16ce