Largely to bring in preprocessor support for additional architectures as based on 6215ba804eb500f3e28b39088c73af3c4f4cd10a by Timothy Gu firstname.lastname@example.org:
Add preprocessor support for additional architectures
- _M_ARM is used by Microsoft 
- __riscv and __riscv_xlen are defined by 
- __sparc and sparc are documented at 
- MIPSEB, PPC, PPC64 are documented at  and used in Chromium's build/build_config.h  Note: Chromium assumes that all PowerPC architectures are 64-bit. This is in fact not true.