Fix for http://omnios.omniti.com/ticket.php/83 'libgmp problems in 151008'

This fixes the unresolved symbol in libgmp.so (__gmpn_invert_limb) as detailed in http://omnios.omniti.com/ticket.php/83 need by some applications (like tesseract-ocr). I must admit that my compiler and linking foo is relativly weak. This fixes the problem for me but I cannot oversee what other consequences adding this flag has.