Fix Unity builds for Fortran and D targets
Fix Unity builds for Fortran and D targets

Also warn if we're trying to use a unity build on a target with fortran
or D sources.

rhd/meson,mesonbuild/meson,mesonbuild/meson,thiblahute/meson,fmuellner/meson,pexip/meson,wberrier/meson,aaronp24/meson,mesonbuild/meson,jeandet/meson,thiblahute/meson,rhd/meson,ernestask/meson,jeandet/meson,fmuellner/meson,wberrier/meson,MathieuDuponchelle/meson,centricular/meson,centricular/meson,fmuellner/meson,thiblahute/meson,pexip/meson,jeandet/meson,fmuellner/meson,QuLogic/meson,pexip/meson,MathieuDuponchelle/meson,rhd/meson,jeandet/meson,pexip/meson,trhd/meson,becm/meson,ernestask/meson,wberrier/meson,ernestask/meson,thiblahute/meson,QuLogic/meson,jpakkane/meson,becm/meson,becm/meson,centricular/meson,jpakkane/meson,trhd/meson,centricular/meson,QuLogic/meson,trhd/meson,aaronp24/meson,mesonbuild/meson,rhd/meson,becm/meson,rhd/meson,wberrier/meson,pexip/meson,centricular/meson,jpakkane/meson,MathieuDuponchelle/meson,QuLogic/meson,MathieuDuponchelle/meson,mesonbuild/meson,trhd/meson,becm/meson,jpakkane/meson,jpakkane/meson,becm/meson,pexip/meson,jpakkane/meson,trhd/meson,wberrier/meson,rhd/meson,trhd/meson,trhd/meson,thiblahute/meson,jeandet/meson,centricular/meson,jpakkane/meson,rhd/meson,ernestask/meson,trhd/meson,becm/meson,becm/meson,becm/meson,QuLogic/meson,rhd/meson,aaronp24/meson,mesonbuild/meson,aaronp24/meson,fmuellner/meson,thiblahute/meson,ernestask/meson,jeandet/meson,pexip/meson,pexip/meson,MathieuDuponchelle/meson,aaronp24/meson,QuLogic/meson,QuLogic/meson,pexip/meson,trhd/meson,mesonbuild/meson,ernestask/meson,fmuellner/meson,jpakkane/meson,jeandet/meson,fmuellner/meson,aaronp24/meson,ernestask/meson,aaronp24/meson,aaronp24/meson,ernestask/meson,thiblahute/meson,aaronp24/meson,wberrier/meson,thiblahute/meson,fmuellner/meson,MathieuDuponchelle/meson,becm/meson,fmuellner/meson,mesonbuild/meson,jeandet/meson,MathieuDuponchelle/meson,pexip/meson,QuLogic/meson,centricular/meson,centricular/meson,mesonbuild/meson,MathieuDuponchelle/meson,ernestask/meson,wberrier/meson,jpakkane/meson,thiblahute/meson,wberrier/meson,QuLogic/meson,MathieuDuponchelle/meson,jeandet/meson,mesonbuild/meson