[Libclc-dev] Implement tgamma and some of its dependencies

[Aaron Watry via Libclc-dev]

This series started from my attempt to implement tgamma so that I can use
it eventually for hcc. The amd-builtin implementation of tgamma uses lgamma,
which itself uses lgamma_r. So, in the end, all 3 of these functions have
been ported/implemented.

Note: I'm fairly positive that _CLC_V_V_VP_VECTORIZE was previously unused.
      I don't know that it has ever been used, and I'm fairly confident
      about the address space addition. If anyone has concerns, please let
      me know.