Another attempt to fix MSVC by explicitly disabling the conversion operator when the value type can't be initialized from the argument type. Testing with the online MSVC compiler is finally happy with this, let's see if the build bot will tolerate it.
Another attempt to fix MSVC by explicitly disabling the conversion
operator when the value type can't be initialized from the argument
type. Testing with the online MSVC compiler is finally happy with this,
let's see if the build bot will tolerate it.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@269501 91177308-0d34-0410-b5e6-96231b3b80d8

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