Split implementation files along a uses-libc/shouldn't-use-libc
boundary.
- InstrProfiling.h is a shared header.
- InstrProfiling.c provides an API to extract profiling data from the
runtime, but avoids the use of libc. Currently this is a lie:
__llvm_pgo_write_buffer() uses `FILE*` and related functions. It
will be updated soon to write to a `char*` buffer instead.
- InstrProfilingExtras.c provides a more convenient API for
interfacing with the profiling runtime, but has logic that does (and
will continue to) use libc.
<rdar://problem/15943240>
llvm-svn: 204268
