[X86][SSE] Rename truncateVectorCompareWithPACKSS to truncateVectorWithPACKSS. NFC.
[X86][SSE] Rename truncateVectorCompareWithPACKSS to truncateVectorWithPACKSS. NFC.

We no longer rely on the vector source being a comparison result, just have sufficient sign bits.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@316834 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm