[builtin] for the condition for check __ARM_FEATURE_CLZ

Summary: Since CLZ is not available for Thumb1, we use __ARM_ARCH_ISA_THUMB != 1 as one of the conditions.

Reviewers: rnk, compnerd, rengolin

Subscribers: aemerson, rengolin, llvm-commits

Differential Revision: https://reviews.llvm.org/D27530

llvm-svn: 288954