build: Cleanup disabled warnings a bit
build: Cleanup disabled warnings a bit

Some C-specific warnings were turned off as the spice module used to
ship a C++ spice client. It's long gone, so we can reenable these
warnings.
There were warnings disabled for tunnel support and CEGUI usage which
have both been removed too.
-Wno-format-nonliteral was disabled twice.

Acked-by: Frediano Ziglio <55d48b080b2e443e395cde84d2c83b135a4ff48e@redhat.com>

fgouget/spice,fgouget/spice,fgouget/spice,fgouget/spice