Fix another really nasty regression that Anshu pointed out.  In cases where dangling constant users were removed from a function, causing it to be dead, we never removed the call graph edge from the external node to the function.
Fix another really nasty regression that Anshu pointed out.  In cases where
dangling constant users were removed from a function, causing it to be dead,
we never removed the call graph edge from the external node to the function.

In most cases, this didn't cause a problem (by luck).  This should definitely
go into 1.3


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@15570 91177308-0d34-0410-b5e6-96231b3b80d8

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