Support for non-default rounding modes in the softfloat layer

[Joerg Sonnenberger <joerg%britannica.bec.de@localhost>]

Hi all,
one major difference between the existing softfloat support in libc and
compiler-rt's softfloat implementation is the (non)support for
rounding modes. libc supports some global variables for that, which is
of limited usefulness in a multi-threaded world. Making them fully
thread-local on the other hand is quite expensive. A discussion with the
responsible developer of the compiler-rt code and some LLVM folks
resulting in the suggestion of providing an alternative set of entry
points, where the float environment is an explicit argument, if this
feature is really desirable. Long story short, does anyone use
non-default rounding modes on platforms with softfloat?

Joerg