Fix to handle all non-power-of-2 vector sizes in the mask form of _builtin_shuffle_vector.

Previously a 2-bit mask was used to mask each element of a vec6 mask before doing the extracts instead of 3-bit mask necessary to cover 0-5. vec3 was the only non-power-of-2 that worked correctly because a +1 conditionally added before calculating floor(log2(elements)).



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187560 91177308-0d34-0410-b5e6-96231b3b80d8