WasmFS: Fix preload-files forcing the filesystem (#19562)

The bug fixed here is that the preloading logic for setting FORCE_FILESYSTEM must appear
before the WasmFS code that reads it. This just moves code upwards (and enables
a test that shows the problem).

Author: kripken

emcc.py

@@ -2297,6 +2297,12 @@ def phase_linker_setup(options, state, newargs):
   if not settings.GL_SUPPORT_SIMPLE_ENABLE_EXTENSIONS and settings.GL_SUPPORT_AUTOMATIC_ENABLE_EXTENSIONS:
     exit_with_error('-sGL_SUPPORT_SIMPLE_ENABLE_EXTENSIONS=0 only makes sense with -sGL_SUPPORT_AUTOMATIC_ENABLE_EXTENSIONS=0!')
 
+  if options.use_preload_plugins or len(options.preload_files) or len(options.embed_files):
+    if settings.NODERAWFS:
+      exit_with_error('--preload-file and --embed-file cannot be used with NODERAWFS which disables virtual filesystem')
+    # if we include any files, or intend to use preload plugins, then we definitely need filesystem support
+    settings.FORCE_FILESYSTEM = 1
+
   if settings.WASMFS:
     if settings.NODERAWFS:
       # wasmfs will be included normally in system_libs.py, but we must include
@@ -2374,12 +2380,6 @@ def phase_linker_setup(options, state, newargs):
   if settings.SIDE_MODULE and 'GLOBAL_BASE' in user_settings:
     exit_with_error('GLOBAL_BASE is not compatible with SIDE_MODULE')
 
-  if options.use_preload_plugins or len(options.preload_files) or len(options.embed_files):
-    if settings.NODERAWFS:
-      exit_with_error('--preload-file and --embed-file cannot be used with NODERAWFS which disables virtual filesystem')
-    # if we include any files, or intend to use preload plugins, then we definitely need filesystem support
-    settings.FORCE_FILESYSTEM = 1
-
   if settings.PROXY_TO_WORKER or options.use_preload_plugins:
     settings.DEFAULT_LIBRARY_FUNCS_TO_INCLUDE += ['$Browser']
 

test/test_browser.py

@@ -3525,6 +3525,7 @@ def test_modularize_init_error(self):
 
   # test illustrating the regression on the modularize feature since commit c5af8f6
   # when compiling with the --preload-file option
+  @also_with_wasmfs
   def test_modularize_and_preload_files(self):
     self.set_setting('EXIT_RUNTIME')
     # TODO(sbc): Fix closure warnings with MODULARIZE + WASM=0