[OpenCL] Add memory_scope_all_devices

Add the `memory_scope_all_devices` enum value, which is restricted to
OpenCL 3.0 or newer and the `__opencl_c_atomic_scope_all_devices`
feature.  Also guard `memory_scope_all_svm_devices` accordingly, which
is already available in OpenCL 2.0.

The `__opencl_c_atomic_scope_all_devices` feature is header-only, so
set its define to 1 in `opencl-c-base.h`.  This is done
unconditionally at the moment, as the mechanism for disabling
header-only options hasn't been decided yet.

This patch only adds a negative test for now.  Ideally adding a CL3.0
run line to atomic-ops.cl should suffice as a positive test, but we
cannot do that yet until (at least) generic address spaces and program
scope variables are supported in OpenCL 3.0 mode.

Differential Revision: https://reviews.llvm.org/D103241