meson: find libjpeg via pkg-config

This effectively (but optionally) requires libjpeg-turbo which
ships with a .pc file and is what pretty much everyone these days
uses anyway for libjpeg, so shouldn't be a problem hopefully.

https://bugzilla.gnome.org/show_bug.cgi?id=796947

REQUIREMENTS

@@ -110,7 +110,7 @@ Notes:          This dependency is entirely optional, the video4linux plugin
 
 Package:        JPEG library
 Plugins:        jpeg (jpegenc, jpegdec, smokeenc, smokedec)
-DebianPackage:  libjpeg-dev
+DebianPackage:  libjpeg62-turbo-dev
 URL:            http://www.libjpeg-turbo.org/
                 or http://www.ijg.org/ for the IJG version
 

ext/jpeg/meson.build

@@ -4,7 +4,7 @@ jpeg_sources = [
   'gstjpegdec.c',
 ]
 
-jpeglib = cc.find_library('jpeg', required : get_option('jpeg'))
+jpeglib = dependency('libjpeg', required : get_option('jpeg'))
 
 if jpeglib.found()
   gstjpeg = library('gstjpeg',