We do not currently track the source locations for exception specifications such that their source range can be queried through the AST. This leads to trying to write more complex code to determine the source range for uses like FixItHints (see D18575 for an example). In addition to use within tools like clang-tidy, I think this information may become more important to track as exception specifications become more integrated into the type system.
One thing this patch is missing is a test case. I'm not certain of the best way to test this functionality in isolation; suggestions welcome.