[patch] Add toplevel configure check for MPFR

[Gabriel Dos Reis]

"Joseph S. Myers" <jsm@polyomino.org.uk> writes:

| On Sun, 25 Jul 2004, Paul Brook wrote:
| 
| > Gfortran currently requires GMP (GNU Multiple Precision library) for 
| > compile-time arithmetic. In order to accurately match target arithmetic we 
| > also require MPFR. MPFR is part of GMP, although it is not always enabled.
| 
| Note also that the GMP home page <http://www.swox.com/gmp/> says that "In
| the next major GMP release, mpfr will not be included.  Users are
| encouraged to download mpfr directly from that project's site.".  This may
| only be of relevance to the documentation, not the configure tests, though
| it would complicate importing GMP into GCC (i.e. we'd need to import both
| GMP and MPFR) if we wish to use it outside the Fortran front end (for more
| general constant folding of built-in functions).

Why would we need it all at? (apart from Gfortran is using it at the
moment?).

-- Gaby