meson: Add configuration option to build the cam application

Building the cam application isn't always desired, for instance in a
production environment that only needs the libcamera library. Add a
meson option to disable it.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/cam/meson.build

@@ -1,9 +1,8 @@
 # SPDX-License-Identifier: CC0-1.0
 
-libevent = dependency('libevent_pthreads', required : false)
+libevent = dependency('libevent_pthreads', required : get_option('cam'))
 
 if not libevent.found()
-    warning('libevent_pthreads not found, \'cam\' application will not be compiled')
     subdir_done()
 endif