[clang-format] Only add pragma continuation indentation for 'omp' clauses

The patch in D136100 added custom handling for pragmas to assist in
formatting OpenMP clauses correctly. One of these changes added extra
indentation. This is desirable for OpenMP pragmas as they are several
complete tokens that would otherwise we on the exact same line. However,
this is not desired for the other pragmas.

This solution is extremely hacky, I'm not overly familiar with the
`clang-format` codebase. A better solution would probably require
actually parsing these as tokens, but I just wanted to propose a
solution.

Fixes https://github.com/llvm/llvm-project/issues/59473

Reviewed By: HazardyKnusperkeks

Differential Revision: https://reviews.llvm.org/D144884