Issue #61 - Reinstate buildability with shared gkmedias dll

This fully works for splitting gkmedias.dll back out from xul with one exception
which is Skia throwing undefined externals when linking gkmedias.

modules/brotli/moz.build

@@ -25,6 +25,9 @@ SOURCES += [
     'dec/state.c',
 ]
 
+if CONFIG['GKMEDIAS_SHARED_LIBRARY']:
+    NO_VISIBILITY_FLAGS = True
+
 # We allow warnings for third-party code that can be updated from upstream.
 ALLOW_COMPILER_WARNINGS = True
 
@@ -36,6 +39,8 @@ CFLAGS += ['-DBROTLI_BUILD_PORTABLE']
 
 Library('brotli')
 
+FINAL_LIBRARY = 'gkmedias'
+
 HostProgram('brotli')
 
 HOST_SOURCES += SOURCES