Inlining often produces landingpad instructions with repeated

catch or repeated filter clauses.  Teach instcombine a bunch
of tricks for simplifying landingpad clauses.  Currently the
code only recognizes the GNU C++ and Ada personality functions,
but that doesn't stop it doing a bunch of "generic" transforms
which are hopefully fine for any real-world personality function.
If these "generic" transforms turn out not to be generic, they
can always be conditioned on the personality function.  Probably
someone should add the ObjC++ personality function.  I didn't as
I don't know anything about it.

llvm-svn: 140852