[OpenMP][test] Support target= in tests (#142380)

LLVM is moving towards the `target=<target triple RE>` syntax in `XFAIL:
` etc., and I'll need the same in a subsequent patch.

This patch adds the necessary infrastructure.

Tested on `sparc-sun-solaris2.11`, `sparcv9-sun-solaris2.11`,
`sparc-unknown-linux-gnu`, `sparc64-unknown-linux-gnu`,
`i386-pc-solaris2.11`, `amd64-pc-solaris2.11`, `i686-pc-linux-gnu`, and
`x86_64-pc-linux-gnu`.

GitOrigin-RevId: c450dd7e8398ffa2c17ae80a21a965bc74fc94dd
7 files changed