C ABI and compiler rt improvements for ARM

* add __multi3 compiler rt function. See #1290
* compiler rt includes ARM functions for thumb and aarch64 and
  other sub-arches left out. See #1526
* support C ABI for returning structs on ARM. see #1481
3e72411db0Andrew Kelley committed on 10/13/2018, 7:18:00 PMparent67fb4d1
5 files changedLine totals unavailable