MinGW5.3 ld.exe .rsrc merge failure: duplicate leaf

[jeetee]

resfile.o is already included via object1.rsp, there should be no need to explicitly link it again

See discovery thread https://musescore.org/en/node/181796

[lasconic]

Brilliant !

[Jojo-Schmitz]

I wondered whether this would be beneficial to the 2.2 branch too, so I checked and 2.2 does build with this commit being cherry-picked (there's a conflict due to some formatting/indenting changes though, but that is easy to resolve)
But see yourself in #3437, we'll see whether Travis and AppVeyor are happy with it ;-)