complibs/mpfr: add latest version 2.4.2

Note: the MPFR site happens to be down at the time I wrote
this message, and happens to be down quite often.

Once it's back up'n'runnin', I'll mirror as much as possible
the MPFR tarballs on my site, but in the meantime, you'll
have to handle it by yourself (patience...).

 # ia64 specific config options

 # depends on EXPERIMENTAL

 config ARCH_ia64

     select ARCH_SUPPORTS_64

     select ARCH_USE_MMU

     select ARCH_SUPPORTS_BOTH_ENDIAN

     help

       The ia64 architecture, as defined by:

         http://www.intel.com/design/itanium/arch_spec.htm