[Sanitizer] Enable POSIX regex api on FreeBSD.

Reviewers: krytarowski

Reviewed By: krytarowski

Differential Revision: https://reviews.llvm.org/D56009

M    lib/sanitizer_common/sanitizer_common_interceptors.inc
M    lib/sanitizer_common/sanitizer_platform_interceptors.h
M    lib/sanitizer_common/sanitizer_platform_limits_freebsd.cc
M    lib/sanitizer_common/sanitizer_platform_limits_freebsd.h
D    test/sanitizer_common/TestCases/NetBSD/regex.cc
A  + test/sanitizer_common/TestCases/Posix/regex.cc

llvm-svn: 350002