[CodeGen] Teach SimplifyPersonality about the updated LandingPadInst

When uses of personality functions were moved from LandingPadInst to
Function, we forgot to update SimplifyPersonality(). This patch corrects
that.

Note: SimplifyPersonality() is an optimization which replaces
personality functions with the default C++ personality when possible.
Without this update, some ObjC++ projects fail to link against C++
libraries (seeing as the exception ABI had effectively changed).

rdar://problem/22155434

llvm-svn: 247421