InstrProf: Remove MSVC-specific logic

Apparently, MSVC has stdint.h now?  Let's see if the buildbots complain.
I'm not convinced that the build system is even set up for MSVC to build
this file, but...

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@204515 91177308-0d34-0410-b5e6-96231b3b80d8