[clang] Switch arm-mve-intrinsics tests to use %clang_cc1.

It isn't really necessary for them to run the clang driver, and it's
more efficient not to (and also more stable against driver changes).
Now they invoke cc1 directly, more like the analogous NEON tests.

Reviewers: dmgreen

Subscribers: kristof.beyls, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D69426