valac: Add --use-fast-vapi commandline argument
valac: Add --use-fast-vapi commandline argument

Accepts an input file that was previously produced with the --fast-vapi=
commandline argument.

GNOME/vala,tjol/vala-tjol,rvu95/vala,playya/vala,GNOME/vala,Distrotech/vala,jessevdk/vala,flobrosch/vala-fixes,tjol/vala-tjol,frida/vala,kamanashisroy/aroop,spidermonkdust/vala,tjol/vala-tjol,rvu95/vala,severinh/vala,frida/vala,xdave/pvala,kamanashisroy/aroop,frida/vala,spidermonkdust/vala,jessevdk/vala,GNOME/vala,playya/vala,flobrosch/vala-fixes,frida/vala,Distrotech/vala,kamanashisroy/aroop,Distrotech/vala,GNOME/vala,severinh/vala,frida/vala,spidermonkdust/vala,playya/vala,severinh/vala,flobrosch/vala-fixes,jessevdk/vala,rvu95/vala