Integrate LLVM/GCC Sanitizers with pkgsrc

Contact: tech-pkg@
Mentors: kamil@ + ?
Duration estimate: 3 months

Add support in the pkgsrc framework for building packages with sanitizers.

Target NetBSD/amd64 and LLVM or GCC.

Expected sanitizer options:
 - Address (ASan),
 - Memory (MSan),
 - MemoryWithOrigin (MSan with tracking the origin)
 - Undefined (UBSan),
 - Thread (TSan),
 - Address;Undefined (ASan & UBSan)
 - "" (empty string) - the default option

Milestones:

 1. Ensure the availability of the toolchain and prebuilt userland with the sanitizers.
 2. Add new option in pkgsrc to build the packages with a each sanitizer.
 3. Build the packages and report problems and bugs.