Add support for emitting libcalls for x86_fp80 -> fp128 and vice-versa

compiler_rt doesn't provide them (yet), but libgcc does. PR34076.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@322772 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed