InstrProf: Indicate pointer size in raw profile

Since the profile can come from 32-bit machines, the reader needs to
check the pointer size.  Change the magic number to facilitate this.

<rdar://problem/16400648>
InstrProf: Check pointer size in raw profile

Since the profile can come from 32-bit machines, we need to check the
pointer size.  Change the magic number to facilitate this.

Adds tests for reading 32-bit and 64-bit binaries (both big- and
little-endian).  The tests write a binary using printf in RUN lines
(like raw-magic-but-no-header.test).  Assuming the bots don't complain,
this seems like a better way forward for testing RawInstrProfReader than
committing binary files.

<rdar://problem/16400648>