1. Adds the command line flag for clzero.
2. Includes the clzero flag under znver1.
3. Defines the macro for clzero.
4. Adds a new file which has the intrinsic definition for clzero instruction.
Patch by Ganesh Gopalasubramanian with some additional tests from me.
Differential revision: https://reviews.llvm.org/D29386
llvm-svn: 294559