Summary: Removed platform-specific ifdefs for linux, mac, freebsd and netbsd from sanitizer_procmaps.h

Patch by Yicheng Wang <yichengfb@fb.com>

Reviewers: kcc, kubamracek, alekseyshl, fjricci, vitalybuka

Reviewed By: fjricci, vitalybuka

Subscribers: vitalybuka, emaste, krytarowski, llvm-commits

Differential Revision: https://reviews.llvm.org/D38098

llvm-svn: 313999