Add a specific flag to enable / disable the use of 'import.meta.url' (emscripten-core#9234)

This fixes the problem reported by emscripten-core#9233 and by emscripten-core#8729 while fixing the
    regression bug causes by emscripten-core#8940

Author: adevress

AUTHORS

@@ -422,3 +422,4 @@ a license to everyone to use it as detailed in LICENSE.)
 * Egor Suvorov <[email protected]> (copyright owned by think-cell Software GmbH)
 * James Kuszmaul <[email protected]>
 * Wei Mingzhi <[email protected]>
+* Adrien Devresse <[email protected]>

emcc.py

@@ -3043,7 +3043,7 @@ def modularize():
       # immediately anyhow, like in non-modularize mode)
       # In EXPORT_ES6 + USE_PTHREADS the 'thread' is actually an ES6 module webworker running in strict mode,
       # so doesn't have access to 'document'. In this case use 'import.meta' instead.
-      if shared.Settings.EXPORT_ES6 and shared.Settings.USE_PTHREADS:
+      if shared.Settings.EXPORT_ES6 and shared.Settings.USE_ES6_IMPORT_META:
         script_url = "import.meta.url"
       else:
         script_url = "typeof document !== 'undefined' && document.currentScript ? document.currentScript.src : undefined"

src/settings.js

@@ -941,6 +941,11 @@ var SEPARATE_ASM_MODULE_NAME = '';
 // be enabled for ES6 exports.
 var EXPORT_ES6 = 0;
 
+// Use the ES6 Module relative import feature 'import.meta.url'
+// to auto-detect WASM Module path.
+// It might not be supported on old browsers / toolchains
+var USE_ES6_IMPORT_META = 1;
+
 // If 1, will just time how long main() takes to execute, and not print out
 // anything at all whatsoever. This is useful for benchmarking.
 var BENCHMARK = 0;