Import compiler-rt r215309. Extends 128bit IEEE support in soft-float,
uses Thumb mode by default on ARM when available and fixes a bug in the
division code for ARMs with hardware integer division.

Import compiler-rt r208593. Fix a build bug in __clear_cache by not
explicitly forcing the ABI. Add first part of IEEE 754 quad support.

Import compiler-rt r202303. Extend 128bit support to all LP64 platforms.

Initial import of a cut-down copy of compiler-rt revision r185671.