Add instrastructure for IEEE quad precision.
Based on patch from GuanHong Liu.

Differential Revision: http://llvm-reviews.chandlerc.com/D2796


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@204999 91177308-0d34-0410-b5e6-96231b3b80d8