You either add /usr/local/lib and/or /usr/local/lib64 to $LD_LIBRARY_PATH, or add them to /etc/ld.so.conf, or (since you already have /usr/lib64/libgmp.so.3) add a missing symbolic link:
cd /usr/lib64
sudo ln -s libgmp.so.3 libgmp.so
(and perhaps the same for /usr/lib).
Note that /usr/lib64/libgmp.so.3 might be a different version from /usr/local/lib64/libgmp.so, make sure ghc can actually be used with the former.