This patch does the following.
- Adds an Intrinsic int_x86_clzero which works with __builtin_ia32_clzero
- Identifies clzero feature using cpuid info. (Function:8000_0008, Checks if EBX=1)
- Adds the clzero feature under znver1 architecture.
- The custom inserter is added in Lowering.
- A testcase is added to check the intrinsic.
- The clzero instruction is added to assembler test.