[Statepoints][NFC] Add Statepoint::operator bool()
[Statepoints][NFC] Add Statepoint::operator bool()

Summary:
This allows the "if (Statepoint SP = Statepoint(I))" idiom.

(I don't think this change needs review, this was uploaded to
phabricator to provide context for later dependent changes.)

Differential Revision: http://reviews.llvm.org/D10629

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@241232 91177308-0d34-0410-b5e6-96231b3b80d8

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