Adding a shufflevector and select LLVM IR instructions fuzz tool

Based on similar python tool - utils/shuffle-fuzz.py - this tool extends the ability of it's previous by optionally attaching select instruction to the generated shufflevector instructions.
This was mainly developed to perform exhaustive testing of the X86 AVX512 masked shuffle instructions. But yet it can be used for various other targets.
The general design of the implementation is much modular than the original shuffle_fuzz.py tool, which makes it easier for anyone to extend it further.

Differential Revision: https://reviews.llvm.org/D38031

Change-Id: I0efc2aaa091b61a8a9552311c21cc77916a97111
llvm-svn: 316989