Set of corrections for MSan/NetBSD

Summary:
Changes:

 - Don't attempt to intercept GLIBC specific functions like __strtol_internal.
   This is required to stop intercepting it as we leak dlerror(3) for dlsym(3)
   that cannot manage to find a symbol.
 - Correct interception of fstatat(2).
 - Don't run a test for fgetgrent_r() that is missing on NetBSD.
 - Correct link_map location (offset) in Obj_Entry on x86_64 and i386.
 - Stop intercepting getpshared-like functions in pthread(3). This is feature
   is not enabled by default on NetBSD as it's unfinished.
 - Switch intercepting from UTMP to UTMPX functions.

Sponsored by <The NetBSD Foundation>

Reviewers: joerg, vitalybuka, eugenis, kcc

Reviewed By: vitalybuka

Subscribers: llvm-commits, srhines, kubamracek, #sanitizers

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D41053

llvm-svn: 320663