Fix various issues when building with Visual Studio 2015:
- Visual Studio 2015 adds support for timespec. Add check for
  this and only use our replacement if timespec is not defined.
- Rename lfind/lsearch to my* to avoid redefinition problems.
- Set default value for TMPDIR to "" on Windows as P_tmpdir
  no longer exists.
- timezone and tzname are no renamed _timezone and _tzname.
- std::hash_map has been deprecated, use std::unordered_map instead.
- Add support for Wix Toolset 3.10 which is required to make
  MSI packages with Visual Studio 2015.