Added a ClangUtilityFunction class that allows the

debugger to insert self-contained functions for use by
expressions (mainly for error-checking).

In order to support detecting whether a crash occurred
in one of these helpers -- currently our preferred way
of reporting that an error-check failed -- added a bit
of support for getting the extent of a JITted function
in addition to just its base.

llvm-svn: 112324