rustc_trans: Update LLVMBuildLandingPad signature

rustc_trans: Update LLVMBuildLandingPad signature

The C API of this function changed so it no longer takes a personality function.
A shim was introduced to call the right LLVM function (depending on which
version we're compiled against) to set the personality function on the outer
function.

The compiler only ever sets one personality function for all generated
functions, so this should be equivalent.