Release 4.0.21 (#1638)

With emscripten-releases revisions:

https://chromium.googlesource.com/emscripten-releases/+/d70a5da89b3e673bf6a482724478fc17e81e575e
(LTO)

https://chromium.googlesource.com/emscripten-releases/+/50deeb529cc8a08f952af8a3087d2e27e0f77c3e
(asserts)
diff --git a/bazel/MODULE.bazel b/bazel/MODULE.bazel
index 550c927..9d52644 100644
--- a/bazel/MODULE.bazel
+++ b/bazel/MODULE.bazel
@@ -1,6 +1,6 @@
 module(
     name = "emsdk",
-    version = "4.0.20",
+    version = "4.0.21",
 )
 
 bazel_dep(name = "platforms", version = "0.0.11")
diff --git a/bazel/revisions.bzl b/bazel/revisions.bzl
index a39855a..2be1fb9 100644
--- a/bazel/revisions.bzl
+++ b/bazel/revisions.bzl
@@ -2,6 +2,14 @@
 # DO NOT MODIFY
 
 EMSCRIPTEN_TAGS = {
+    "4.0.21": struct(
+        hash = "d70a5da89b3e673bf6a482724478fc17e81e575e",
+        sha_linux = "e8516b903cd4dc16bf5aa2aacd826adcff5ff1d97d3d88e5e3871decd94cd8b2",
+        sha_linux_arm64 = "415024a22f84424c713b117c3a24cefb98ec03737e02063074010fdc8eaeb334",
+        sha_mac = "f17989b3528cd14971fe75ae9b2aa7d8cc4cc5bbb6d408660e059f822e108a46",
+        sha_mac_arm64 = "7960d8d33243f2f7acdac157136c6e93680550361ed71bb225fcfa25b6bbb2fb",
+        sha_win = "79b3a6b77cf8015cc07ad25353f17f1828e731b0d8757a046071fffbdd5aaf70",
+    ),
     "4.0.20": struct(
         hash = "c387d7a7e9537d0041d2c3ae71b7538cc978104e",
         sha_linux = "a06e7ddda0c168f7ad52e6e0509c98db3545dcb254d3b9052e9e6b8423eaee7d",
diff --git a/emscripten-releases-tags.json b/emscripten-releases-tags.json
index c697cb5..9b604f8 100644
--- a/emscripten-releases-tags.json
+++ b/emscripten-releases-tags.json
@@ -1,6 +1,6 @@
 {
   "aliases": {
-    "latest": "4.0.20",
+    "latest": "4.0.21",
     "latest-sdk": "latest",
     "latest-arm64-linux": "latest",
     "latest-64bit": "latest",
@@ -10,6 +10,8 @@
     "latest-releases-upstream": "latest"
   },
   "releases": {
+    "4.0.21": "d70a5da89b3e673bf6a482724478fc17e81e575e",
+    "4.0.21-asserts": "50deeb529cc8a08f952af8a3087d2e27e0f77c3e",
     "4.0.20": "c387d7a7e9537d0041d2c3ae71b7538cc978104e",
     "4.0.20-asserts": "d4fdf09ba6e7a2d75bc1f643370caf4519021e89",
     "4.0.19": "8b01e2ec3f33e6b94842096d7312ce4ef5f33f6c",