Added OSSetPerformanceMonitor().

[dkosmari]

• Add a declaration for OSSetPerformanceMonitor().
• Define associated enums flags to use as arguments (derived from the PPC manual).
• Define inlined functions to read the performance registers.

[GaryOderNichts]

Also make sure to add the new header to tests/test_compile_headers_common/test_compile_headers_list.h so CI can pick it up.

[GaryOderNichts]

Thanks!