dosbox-staging: enable mt32 emulation support
dosbox-staging: enable mt32 emulation support

MT32 emulation was disabled in ce048c52d717f1b554d6ee09f2fd5dbc40de9641
because it required a dependency not available in Homebrew/core.

`mt32emu` is now available as of aa12751ff3da3a43962fdb6d99a702272feac040
so we no longer need to disable it. This feature is enabled by default.

While we're here, let's enable LTO as recommended by upstream.

Fixes dosbox-staging/dosbox-staging#1270.

Closes #90175.

Signed-off-by: Michka Popoff <5d406f95fb0e0230f83654e4a22d0115cc205d59@users.noreply.github.com>
Signed-off-by: BrewTestBot <8a898ee6867e4f2028e63d2a6319b2224641c06c@users.noreply.github.com>

adam-moss/homebrew-core,chrisfinazzo/homebrew-core,zyedidia/homebrew-core,nbari/homebrew-core,nandub/homebrew-core,sjackman/homebrew-core,Homebrew/homebrew-core,filcab/homebrew-core,filcab/homebrew-core,lemzwerg/homebrew-core,chrisfinazzo/homebrew-core,makigumo/homebrew-core,cblecker/homebrew-core,nandub/homebrew-core,mfikes/homebrew-core,stgraber/homebrew-core,adam-moss/homebrew-core,Homebrew/homebrew-core,zyedidia/homebrew-core,nbari/homebrew-core,makigumo/homebrew-core,stgraber/homebrew-core,uyjulian/homebrew-core,mfikes/homebrew-core,cblecker/homebrew-core,sjackman/homebrew-core,uyjulian/homebrew-core,lemzwerg/homebrew-core