vala: Report warning if --target-glib=auto was not evaluated successfully
vala: Report warning if --target-glib=auto was not evaluated successfully

and don't try to process the valid "auto" string any further.

GNOME/vala,frida/vala,frida/vala,frida/vala,GNOME/vala,frida/vala,GNOME/vala,GNOME/vala,frida/vala