Revert use of import.meta.dirname in the compiler

In emscripten-core#23349 we (I) accidentally broke running emscripten with node older
than v19 and as it happens debian/stable still ships v18:
https://packages.debian.org/bookworm/nodejs

This change reverts emscripten-core#23349 and also explicitly bumps the minimum version
up to v18.20.  I've also added some testing to CI to ensure we can
actually run using this version.

See emscripten-core#23396 and emscripten-core#23407

ChangeLog.md

@@ -20,6 +20,9 @@ See docs/process.md for more on how version tagging works.
 
 4.0.1 (in development)
 ----------------------
+- The mimimum version of node required to run emscripten was bumped from v16.20
+  to v18.20.  Version 4.0 was mistakenly with change that required v20 but that
+  was revered. ()
 
 4.0.0 - 01/14/25
 ----------------

src/utility.mjs

@@ -7,6 +7,7 @@
 // General JS utilities - things that might be useful in any JS project.
 // Nothing specific to Emscripten appears here.
 
+import * as url from 'node:url';
 import * as path from 'node:path';
 import * as fs from 'node:fs';
 import * as vm from 'node:vm';
@@ -230,8 +231,11 @@ export function read(filename) {
   return fs.readFileSync(absolute, 'utf8');
 }
 
+// Use import.meta.dirname here once we drop support for node v18.
+const __dirname = url.fileURLToPath(new URL('.', import.meta.url));
+
 function find(filename) {
-  for (const prefix of [process.cwd(), import.meta.dirname]) {
+  for (const prefix of [process.cwd(), __dirname]) {
     const combined = path.join(prefix, filename);
     if (fs.existsSync(combined)) {
       return combined;

test/test_sanity.py

@@ -286,8 +286,9 @@ def test_node(self):
     for version, succeed in (('v0.8.0', False),
                              ('v4.1.0', False),
                              ('v10.18.0', False),
-                             ('v16.20.0', True),
-                             ('v16.20.1-pre', True),
+                             ('v16.20.0', False),
+                             ('v18.19.0', True),
+                             ('v18.19.1-pre', True),
                              ('cheez', False)):
       print(version, succeed)
       delete_file(SANITY_FILE)

tools/shared.py

@@ -57,9 +57,9 @@
 # Minimum node version required to run the emscripten compiler.  This is
 # distinct from the minimum version required to execute the generated code
 # (settings.MIN_NODE_VERSION).
-# This version currently matches the node version that we ship with emsdk
-# which means that we can say for sure that this version is well supported.
-MINIMUM_NODE_VERSION = (16, 20, 0)
+# This is currently set ot v18.19 since this is the version of node available
+# in debian/stable (bookworm).
+MINIMUM_NODE_VERSION = (18, 19, 0)
 EXPECTED_LLVM_VERSION = 20
 
 # These get set by setup_temp_dirs