Add hard float versions of FP to LL conversions

This adds hard-float implementation for the following builtins:

* __fixdfdi()
* __fixsfdi()
* __fixunsdfdi()
* __fixunssfdi()

The soft-float implementation does never raise floating point
exceptions, which doesn't allow clients to detect floating point
conversion errors.

I must mention that I had to refer to libgcc's implementation to
write these functions.

Related unit-tests of compiler-rt passed with these changes.

Patch was somewhat out-dated, so was updated locally without any
functional changes.

Differential Revision: http://reviews.llvm.org/D5376

llvm-svn: 234148