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...).

# MIPS specific config options

config ARCH_mips

    select ARCH_USE_MMU

    select ARCH_SUPPORTS_BOTH_ENDIAN

    select ARCH_DEFAULT_BE

    select ARCH_SUPPORT_ARCH

    select ARCH_SUPPORT_ABI

    select ARCH_SUPPORT_TUNE

    help

      The MIPS architecture, as defined by:

        http://www.mips.com/