[InstrProf] Port test suite to Windows

Summary:
Before this change, check-profile would run, but all tests would be
marked unsupported on Windows. This is the new status of 'check-profile'
after this change:

Testing Time: 6.66s
  Expected Passes    : 29
  Expected Failures  : 5
  Unsupported Tests  : 39

I moved many tests that exercise posix-y features like dlopen and DSOs
into the Posix subdirectory, and ran the tests on Linux to validate my
changes.

These are the remaining tests that I handled on a case by case basis:
- instrprof-path.c
  Passes, Fixed some path portability issues
- instrprof-gcov-exceptions.test
  Passes, the FileCheck actually succeeds on Windows, so I RUNX'd it
- instrprof-icall-promo.test
  XFAILed, probably due to C++ ABI differences in vtables
- instrprof-merge-match.test
- instrprof-merge.c
- instrprof-merging.cpp
  XFAILed, These seem like real bugs that need fixing
- instrprof-version-mismatch.c
  XFAILed, Overriding the weak version symbol doesn't work
- instrprof-without-libc.c
  UNSUPPORTED, test needs an executable symbol table, Windows has none

Reviewers: davidxl, wmi, void

Subscribers: fedor.sergeev, #sanitizers, llvm-commits

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D57853

llvm-svn: 353435