Drop ancient clang requirement from FIPS builds

[kornelski]

FedRAMP policies have been relaxed, and they allow using newer compilers:

https://github.com/google/boringssl/blob/main/crypto/fipsmodule/FIPS.md#update-stream

[kornelski]

Almost!

I'm running into a build issue on macOS:

error while parsing "…/out/build/libbcm_c_generated_asm.a":
parse error near WS (line 2 symbol 29 - line 2 symbol 30):
"\t"

which looks similar to problems aws-lc has with the delocator hack.