Add codegen test for PGO instrumentation.
This PR adds a codegen test that makes sure that LLVM actually generates instrumentation code when we enable PGO instrumentation in `rustc`.
The second commit updates a test case to the new commandline option syntax introduced in #59874. Without the fix the test still works, but it confusingly creates a directory called `test.profraw`, which usually is the name of the _file_ where profiling data is collected.
Mazdak Farrokhzad
bb892be98e