[crt] Fix inline declarations to work with clang.

This doesn't actually change the generated code in the places
that I looked at as the compiler was already deciding to inline.
[crt] Use likely/unlikely.
[crt] Fix sh syntax in Makefile.

This part of the target is only used on OS X, so the error didn't
break anything previously.
Merge pull request #386 from waywardmonkeys/c-run-time-work

C run time work