export CFLAGS="-march=i486 -mtune=i686 -Os -pipe"
export CXXFLAGS="-march=i486 -mtune=i686 -Os -pipe"

mpfr-2.4.2
----------
patch -N -Z -p1 < ../mpfr_allpatches.patch

./configure --prefix=/usr --enable-shared --with-gmp=/usr

time make
real    1m 3.88s

sudo make install