add -f gcc-6plus

do export CC=gcc or else it will find /usr/bin/x86_64-linux-gnu-gcc and not /mit/gcc-6plus/bin/x86_64-pc-linux-gnu-gcc (the difference is infix "pc").

there is no c++ so LD_RUN_PATH seems unnecessary

configure --disable-aprcl
because deterministic primality testing is very slow: 1300 bit integers 15 seconds versus roughly 0 seconds.

time make ecm-params
real 10m11.794s

for testing whether the prime bug still exists
echo 10^60+7 | /mit/gp/bin/ecm -c 10 -I 1 1e5