[X86][AVX] Rename LowerVectorBroadcast to lowerBuildVectorAsBroadcast. NFCI.

Since the shuffle refactor, this is only used during BUILD_VECTOR lowering.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301834 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed