strerror_r(). Doing this allows us to ensure that strerror_r() always
fills the supplied buffer regardless of EINVAL or ERANGE errors.
strerror()'s semantics have changed slightly such that an argument of
0 is now considered invalid and errno is set to EINVAL.
Remove internal regression test for strerror() and strerror_r(). This
will be reincarnated in src/tools/regression/lib/libc/string.
In strerror(3), add a comment about strerror()'s bogus return type.
PR: 44356
5a98f074e6