[NFC][OpenMP] Use clang_cc1 to driver tests

The test driver-fopenmp-extensions.c is failing on platforms that does
not use integrated-as. It can be reproduced using -fno-integrated-as on
Linux too.

bin/clang -c -Xclang -verify=omp -fopenmp      -fopenmp-extensions
-fno-openmp-extensions
../llvm-project/clang/test/OpenMP/driver-fopenmp-extensions.c
-fno-integrated-as
Assembler messages:
Error: can't open /tmp/driver-fopenmp-extensions-8fafe8.s for reading:
No such file or directory
clang-14: error: assembler command failed with exit code 1 (use -v to
see invocation)

The goal of this test is to verify syntax diags only,
so we should use clang_cc1 to test.

Reviewed By: jdenny, ABataev

Differential Revision: https://reviews.llvm.org/D109255