Add support for invoke/landingpad/resume in C API test

Summary: As per title. There was a lot of part missing in the C API, so I had to extend the invoke and landingpad API.

Reviewers: echristo, joker.eph, Wallbraker

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D17359

llvm-svn: 261254