Fix @opindex for mcall-aixdesc and mcall-openbsd

For mcall-aixdesc, the opindex was just m which was wrong.
For mcall-openbsd, the opindex was mcall-netbsd which was wrong.
This two have been broken since the options were added to the documentation
back in r0-92913-g244609a618b094 .

Committed as obvious after a "make html" and checking the options index.

Thanks,
Andrew

gcc/ChangeLog:

	* doc/invoke.texi: Fix opindex for mcall-aixdesc and mcall-openbsd.
1 file changed