meson: enable bs2b compilation

Add meson build system support to bs2b plugin.

https://bugzilla.gnome.org/show_bug.cgi?id=794346

ext/bs2b/meson.build

@@ -0,0 +1,15 @@
+bs2b_sources = [ 'gstbs2b.c', ]
+
+bs2b_dep = dependency('libbs2b', version : '>=3.1.0', required : false)
+
+if bs2b_dep.found()
+  gstbs2b = library('gstbs2b',
+    bs2b_sources,
+    c_args : gst_plugins_bad_args,
+    link_args : noseh_link_args,
+    include_directories : [configinc, libsinc],
+    dependencies : [gstaudio_dep, gstbase_dep, bs2b_dep],
+    install : true,
+    install_dir : plugins_install_dir,
+  )
+endif

ext/meson.build

@@ -1,6 +1,6 @@
 subdir('assrender')
 subdir('aom')
-#subdir('bs2b')
+subdir('bs2b')
 subdir('bz2')
 subdir('chromaprint')
 subdir('curl')