complibs/mpc: fix MPC 0.8.1 build with MPFR 3.0.0

This is the change introduced by revision 734 of MPC repository.

Author: Paul Zimmermann <Paul.Zimmermann@loria.fr>
Revision log: [acos.c] fixed problem with GMP_RNDA (should be MPFR_RNDA, and code was wrong)

Signed-off-by: Arnaud Lacombe <lacombar@gmail.com>

# Blackfin specific configuration file

config ARCH_blackfin

    select ARCH_SUPPORTS_32

    select ARCH_DEFAULT_32

    select ARCH_DEFAULT_LE

    select ARCH_SUPPORT_ARCH

    select ARCH_SUPPORT_CPU

    select ARCH_SUPPORT_TUNE

    select ARCH_SUPPORT_FPU

     help

      The Blackfin architecture