Add capability to get and set the personalitty function from the C API

Summary:
The capability was lost with D10429 where the personality function was set at function level rather than landing pad level. Now there is no way to get/set the personality function from the C API. That is a problem.

Note that the whole thing could be avoided by improving the C API testing, as started by D10725

Reviewers: chandlerc, bogner, majnemer, andrew.w.kaylor, rafael, rnk, axw

Subscribers: rafael, llvm-commits

Differential Revision: http://reviews.llvm.org/D10946

llvm-svn: 242104