Handle symbol renaming of sigaction for NetBSD

Summary:
NetBSD uses the __sigaction14 symbol name for historical and compat
reasons for the sigaction(2) function name.

Rename the interceptors and users of sigaction to sigaction_symname
and reuse it in the code base.

This change fixes 4 failing tests in TSan/NetBSD:

 - ThreadSanitizer-x86_64 :: signal_errno.cc
 - ThreadSanitizer-x86_64 :: signal_malloc.cc
 - ThreadSanitizer-x86_64 :: signal_sync2.cc
 - ThreadSanitizer-x86_64 :: signal_thread.cc

Sponsored by <The NetBSD Foundation>

Reviewers: joerg, vitalybuka, eugenis, dvyukov, kcc

Reviewed By: dvyukov

Subscribers: kubamracek, llvm-commits, #sanitizers

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D40341

llvm-svn: 319160