[OpenMP][OMPT] A few improvements

This change includes miscellaneous improvements as follows:
1) Added ompt_get_proc_id() implementation for Windows
2) Added parser and print tool for omp-tool-var, just in case it needs
   to be printed (OMP_DISPLAY_ENV)
3) omp_control_tool is exported on Windows

Patch by Hansang Bae

Differential Revision: https://reviews.llvm.org/D50538

llvm-svn: 343137