wasm: build: Use .wasm extension for shared module

This makes sure the shared modules are built with .wasm extension
instead of .so.

However libvlc and libvlccore are still built with .so extension.

m4/vlc.m4

@@ -89,6 +89,9 @@ AC_DEFUN([VLC_LIBRARY_SUFFIX], [
     hpux*)
       LIBEXT=".sl"
       ;;
+    emscripten*)
+      LIBEXT=".wasm"
+      ;;
     *)
       LIBEXT=".so"
       ;;