This reverts commit 11aa31f595325d6b2dede3364e4b86d78fffe635, restoring
commit 055e4319112282354327af9908091fdb25149e9b, with added fixes for
linker unsats.
In some cases multiple calls to different targets may end up with the
same debug information, and therefore callsite id. We will end up
sharing the node between these calls. We don't know which one matches
the callees until all nodes are matched with calls, at which point any
non-matching calls should be removed from the node. The fix extends the
handling in handleCallsitesWithMultipleTargets to do this, and adds
tests for various permutations of this situation.