UPSTREAM: arm64: vdso32: Rename COMPATCC to CC_COMPAT

For consistency with CROSS_COMPILE_COMPAT, mechanically rename COMPATCC
to CC_COMPAT so that specifying aspects of the compat vDSO toolchain in
the environment isn't needlessly confusing.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
(cherry picked from commit eff9cb67be21346402ea07d7a48564909b4f0f25)
Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 154668398
Change-Id: I72f84c27e717a2698c56eede8de0eac9eb3f85e9