ninjabackend: Use 'custom targets' instead of 'CustomTarget' in description
ninjabackend: Use 'custom targets' instead of 'CustomTarget' in description

The build definition is basically cleaning all the directories of all
custom targets.

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