[LoopUnroll] Use IRBuilder to create branch instructions.
[LoopUnroll] Use IRBuilder to create branch instructions.

Use IRBuilder::Create(Cond)?Br instead of constructing instructions
manually with BranchInst::Create(). It's consistent with other
uses of IRBuilder in this pass, and has an additional important
benefit:

Using IRBuilder will ensure that new branch instruction will get
the same debug location as original terminator instruction it will
eventually replace.

For now I'm not adding a testcase, as currently original terminator
instruction also lack debug location due to missing debug location
propagation in BasicBlock::splitBasicBlock. That is, the testcase
will accompany the fix for the latter I'm going to mail soon.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@239550 91177308-0d34-0410-b5e6-96231b3b80d8

GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,dslab-epfl/asap,dslab-epfl/asap,dslab-epfl/asap,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,dslab-epfl/asap,dslab-epfl/asap,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,dslab-epfl/asap