Automatically generate __sig properties for JS library symbols (#18985)

This primary change here is the creation of `emscripten_internal.h`
which is an internal-only header that contains that declaration of
internal JS function that are not already declared in other files.

The reason for this is to ensure that all JS library functions that are
callable form native code have a valid declaration, at least internally,
so that gen_sig_info.py can extract that signature from a compiled wasm
file.

This change add the scripte for generating `library_sigs.js` but doesn't
actually start using it, or erase the correpsonding hand-created `__sig`
entries. That is will be part of a followup

Author: sbc100

src/compiler.js

@@ -21,6 +21,7 @@ global.printErr = (x) => {
 };
 
 function find(filename) {
+  assert(filename);
   const prefixes = [__dirname, process.cwd()];
   for (let i = 0; i < prefixes.length; ++i) {
     const combined = nodePath.join(prefixes[i], filename);
@@ -32,6 +33,7 @@ function find(filename) {
 }
 
 global.read = (filename) => {
+  assert(filename);
   const absolute = find(filename);
   return fs.readFileSync(absolute).toString();
 };
@@ -43,22 +45,25 @@ function load(f) {
 // Basic utilities
 load('utility.js');
 
+// Load default settings
+load('./settings.js');
+load('./settings_internal.js');
 
 const argv = process.argv.slice(2);
 const symbolsOnlyArg = argv.indexOf('--symbols-only');
 if (symbolsOnlyArg != -1) {
   argv.splice(symbolsOnlyArg, 1);
 }
 
-const symbolsOnly = symbolsOnlyArg != -1;
-
 // Load settings from JSON passed on the command line
 const settingsFile = argv[0];
 assert(settingsFile);
 
 const settings = JSON.parse(read(settingsFile));
 Object.assign(global, settings);
 
+global.symbolsOnly = symbolsOnlyArg != -1;
+
 EXPORTED_FUNCTIONS = new Set(EXPORTED_FUNCTIONS);
 WASM_EXPORTS = new Set(WASM_EXPORTS);
 SIDE_MODULE_EXPORTS = new Set(SIDE_MODULE_EXPORTS);
@@ -94,7 +99,7 @@ if (!STRICT) {
 B = new Benchmarker();
 
 try {
-  runJSify(symbolsOnly);
+  runJSify();
 
   B.print('glue');
 } catch (err) {

src/jsifier.js

@@ -66,7 +66,7 @@ function isDefined(symName) {
   return false;
 }
 
-function runJSify(symbolsOnly = false) {
+function runJSify() {
   const libraryItems = [];
   const symbolDeps = {};
   let postSets = [];

src/library.js

@@ -3029,16 +3029,11 @@ mergeInto(LibraryManager.library, {
     return runEmAsmFunction(code, sigPtr, argbuf);
   },
 
-#if MEMORY64
-  // We can't use the alias in wasm64 mode becuase the function signature differs
   emscripten_asm_const_ptr__sig: 'pppp',
   emscripten_asm_const_ptr__deps: ['$runEmAsmFunction'],
   emscripten_asm_const_ptr: function(code, sigPtr, argbuf) {
     return runEmAsmFunction(code, sigPtr, argbuf);
   },
-#else
-  emscripten_asm_const_ptr: 'emscripten_asm_const_int',
-#endif
 
   $runMainThreadEmAsm__deps: ['$readEmAsmArgs'],
   $runMainThreadEmAsm__sig: 'iippi',