Auto merge of #146 - rust-lang-nursery:gh145, r=alexcrichton
Auto merge of #146 - rust-lang-nursery:gh145, r=alexcrichton

fix infinite recursion in divmoddi4 / mulodi4

on ARMv7-M processors, divmoddi4 was calling mulodi4 and mulodi4 was calling
divmoddi4 leading to infinite recursion. This commit breaks the cycle by using
wrapping multiplication in divmoddi4.

fixes #145

r? @alexcrichton

japaric/rustc-builtins,japaric/rustc-builtins