[Dominators] Workaround explicit instantiation bug.
[Dominators] Workaround explicit instantiation bug.

Some platforms have problems with emmiting constructors when class
templates get explicitly instantiated.
This patch fixes the bug reported in D35315 by replacing `= default`
with an empty constructor body.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@308140 91177308-0d34-0410-b5e6-96231b3b80d8

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