Add obsolete 8087 and 287 instructions and remove compiler warning

Add entries in optable.xml for obsolete 8087 instructions FNENI (DB E0), FNDISI (DB E1), FNSETPM (DB E4), and FRSTPM (DB E5). All but the latter execute (as NOPs) on modern CPUs.  Also remove not standalone condition on string.h in udis86.c. It's required for memset at udis86.c:47.