Split lgammal() from INIT_LGAMMAL

Summary:
Introduce SANITIZER_INTERCEPT_LGAMMAL
dedicated for lgammal(). Disable it for NetBSD
as this routine is not implemented in this OS.

Installation of supernumerary interceptors causes
leaking of errors to dlsym(3)-like operations.

Reviewers: joerg, vitalybuka

Reviewed By: vitalybuka

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

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D54054

llvm-svn: 346352