Is your libgmp.so a current version? (As -lgmp is on the link command line, and you didn't get an error, some version of libgmp appears to have been found...)   You could check with dump whether the (shared) lib provides the symbols in question, e.g.

$ dump -T /usr/local/lib/libgmp.so | grep ...
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(The -T option is from memory (I don't have an AIX system here at the moment). Use nm instead of dump in case you have a static library. See the respective man pages in case of doubt...)