Fixed gcc-fat.sh failing to build Objective-C sources correctly.

This would fail if the compiler was given a .m file _and_ no "-o" option; it
would fail to automatically calculate the correct .o filename in this
situation.

Thanks to Ethan Lee for the help tracking this one down!

--HG--
extra : rebase_source : 3620d161d8c52613e864e156379837db5b8b0be6