Allow proper compilation with --enable-shared

Enables compilation of vlc with wasm32-unknown-emscripten with shared module. Previously compilation would fail because of various compatibility issues, Like:

• Incompatible dependencies from c++ sources
• Test binaries not marked with -s MAIN_MODULE when building
• Building modules did not have exported symbols
• Contribs were not built with pthread/atomics

bin/Makefile.am

@@ -19,6 +19,9 @@ AM_CFLAGS = $(CFLAGS_vlc)
 if HAVE_DBUS
 AM_CPPFLAGS += -DHAVE_DBUS
 endif
+if HAVE_EMSCRIPTEN
+AM_CFLAGS += -sMAIN_MODULE=1
+endif
 
 #
 # Main VLC executable