[Clang, SystemZ] Split test into Driver and CodeGen parts (NFC) (#79808)

The test added in #73511 currently fails in
CLANG_DEFAULT_PIE_ON_LINUX=OFF configuration, because it uses the clang
driver in a codegen test.

Split the test into two, a driver test that checks that the appropriate
target feature is passed, and a codegen test that uses cc1.