[dsymutil] Fix assertion triggered by empty address range.
[dsymutil] Fix assertion triggered by empty address range.

An assertion was hit when running dsymutil on a gcc generated binary
that contained an empty address range. Address ranges are stored in an
interval map of half open intervals. Since the interval is empty and
therefore meaningless, we simply don't add it to the map.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@350591 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit 8ece8d35864e0aa62e7c91919b8e2e931bc29105)

apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm