[PATCH] [COMPILER-RT] Enable __multi3 when using aarch64 architecture

[Tim Northover]

  Only __multi3? It looks like we emit __divti3 and __modti3 as well.

  Compares, adds and subtracts should be inlined by Clang, and amusingly we assert for at least some shifts but it *looks* like we'd inline them if that was fixed. Though, of course, other compilers may be different.

http://llvm-reviews.chandlerc.com/D2801