clang-format libc string functions imported from musl

[emaste]

Summary

We have adopted these and don't consider them 'contrib' code.

[emaste]

lib/libc/string/strcspn.c

31–32

splitting between the 1 and << seems confusing

[emaste]

I much prefer the formatted version, except perhaps for the BITOP macro.

We have adopted these functions; changes from musl, if any, would be manually applied if this change goes in.
OpenBSD also imported some musl string routines and reformatted them.

[arichardson]

lib/libc/string/strcspn.c

31–32

Seems like clang-format assumes that op( is a function call and then the formatting for the rest of the line is broken.
It might also like breaking before << because of LLVM's streaming I/O classes where that formatting does make sense.

[emaste]

(Original review to import these string functions was still open in D17630; we imported other musl string functions in rS315467, rS346054, rS351700)

[emaste]

strchr and strchrnul imported in 7f72497ef756ff7d03d5560c2d1c1f92f73fcb52, already formatted
strcspn was dropped from D17630