Mark the SOURCES variables in media/mtransport moz.build files as non-unifiable, no bug

DONTBUILD

media/mtransport/build/moz.build

@@ -26,6 +26,7 @@ EXPORTS.mtransport += [
 
 include('../objs.mozbuild')
 
+# These files cannot be built in unified mode because they force NSPR logging.
 SOURCES += mtransport_cppsrcs
 
 LIBRARY_NAME = 'mtransport'

media/mtransport/standalone/moz.build

@@ -6,6 +6,7 @@
 
 include('../objs.mozbuild')
 
+# These files cannot be built in unified mode because they force NSPR logging.
 SOURCES += mtransport_cppsrcs
 
 LIBRARY_NAME = 'mtransport_s'