Remove FS.genericErrors. NFC (emscripten-core#22914)

This system was introduced in 2013 (see 1844811) but never more widely
adopted.

Author: sbc100

src/library_fs.js

@@ -63,7 +63,6 @@ FS.staticInit();
     trackingDelegate: {},
 #endif
     ErrnoError: null, // set during init
-    genericErrors: {},
     filesystems: null,
     syncFSRequests: 0, // we warn if there are multiple in flight at once
 #if expectToReceiveOnModule('logReadFiles')
@@ -1435,12 +1434,6 @@ FS.staticInit();
 #endif
     },
     staticInit() {
-      // Some errors may happen quite a bit, to avoid overhead we reuse them (and suffer a lack of stack info)
-      [{{{ cDefs.ENOENT }}}].forEach((code) => {
-        FS.genericErrors[code] = new FS.ErrnoError(code);
-        FS.genericErrors[code].stack = '<generic error, no stack>';
-      });
-
       FS.nameTable = new Array(4096);
 
       FS.mount(MEMFS, {}, '/');

src/library_memfs.js

@@ -6,6 +6,15 @@
 
 addToLibrary({
   $MEMFS__deps: ['$FS', '$mmapAlloc'],
+#if !ASSERTIONS
+  $MEMFS__postset: `
+    // This error may happen quite a bit. To avoid overhead we reuse it (and
+    // suffer a lack of stack info).
+    MEMFS.doesNotExistError = new FS.ErrnoError({{{ cDefs.ENOENT }}});
+    /** @suppress {checkTypes} */
+    MEMFS.doesNotExistError.stack = '<generic error, no stack>';
+    `,
+#endif
   $MEMFS: {
     ops_table: null,
     mount(mount) {
@@ -173,7 +182,11 @@ addToLibrary({
         }
       },
       lookup(parent, name) {
-        throw FS.genericErrors[{{{ cDefs.ENOENT }}}];
+#if ASSERTIONS
+        throw new FS.ErrnoError({{{ cDefs.ENOENT }}});
+#else
+        throw MEMFS.doesNotExistError;
+#endif
       },
       mknod(parent, name, mode, dev) {
         return MEMFS.createNode(parent, name, mode, dev);

test/other/codesize/test_codesize_cxx_ctors1.gzsize

@@ -1 +1 @@
-8465
+8447

test/other/codesize/test_codesize_cxx_ctors1.jssize

@@ -1 +1 @@
-20821
+20791

test/other/codesize/test_codesize_cxx_ctors2.gzsize

@@ -1 +1 @@
-8449
+8432

test/other/codesize/test_codesize_cxx_ctors2.jssize

@@ -1 +1 @@
-20789
+20759

test/other/codesize/test_codesize_cxx_except.gzsize

@@ -1 +1 @@
-9487
+9474

test/other/codesize/test_codesize_cxx_except.jssize

@@ -1 +1 @@
-24665
+24634

test/other/codesize/test_codesize_cxx_except_wasm.gzsize

@@ -1 +1 @@
-8427
+8414

test/other/codesize/test_codesize_cxx_except_wasm.jssize

@@ -1 +1 @@
-20715
+20685