Apply the set of system JS libraries based on the link settings via a…

… code path in shared.Building.

emcc.py

@@ -943,11 +943,8 @@ def detect_fixed_language_mode(args):
           system_js_libraries += shared.Building.path_to_system_js_libraries(lib)
 
       # Certain linker flags imply some link libraries to be pulled in by default.
-      if 'EMTERPRETIFY_ASYNC=1' in settings_changes: system_js_libraries += ['library_async.js']
-      if 'ASYNCIFY=1' in settings_changes: system_js_libraries += ['library_async.js']
-      if 'LZ4=1' in settings_changes: system_js_libraries += ['library_lz4.js']
-      if 'USE_SDL=1' in settings_changes: system_js_libraries += ['library_sdl.js']
-      if 'USE_SDL=2' in settings_changes: system_js_libraries += ['library_egl.js', 'library_glut.js', 'library_gl.js']
+      system_js_libraries += shared.Building.path_to_system_js_libraries_for_settings(settings_changes)
+
       settings_changes.append('SYSTEM_JS_LIBRARIES="' + ','.join(system_js_libraries) + '"')
 
       # If not compiling to JS, then we are compiling to an intermediate bitcode objects or library, so

tools/shared.py

@@ -2043,6 +2043,18 @@ def path_to_system_js_libraries(library_name):
 
     return library_files
 
+  @staticmethod
+  # Given a list of Emscripten link settings, returns a list of paths to system JS libraries
+  # that should get linked automatically in to the build when those link settings are present.
+  def path_to_system_js_libraries_for_settings(link_settings):
+    system_js_libraries =[]
+    if 'EMTERPRETIFY_ASYNC=1' in link_settings: system_js_libraries += ['library_async.js']
+    if 'ASYNCIFY=1' in link_settings: system_js_libraries += ['library_async.js']
+    if 'LZ4=1' in link_settings: system_js_libraries += ['library_lz4.js']
+    if 'USE_SDL=1' in link_settings: system_js_libraries += ['library_sdl.js']
+    if 'USE_SDL=2' in link_settings: system_js_libraries += ['library_egl.js', 'library_glut.js', 'library_gl.js']
+    return system_js_libraries
+
 # compatibility with existing emcc, etc. scripts
 Cache = cache.Cache(debug=DEBUG_CACHE)
 chunkify = cache.chunkify