Revert "Roll emsdk to 4.0.20"

This reverts commit cf78ce87c4b1b066e651df5560b7cdf3f502bfc0.

Reason for revert: breaks on GN build (I forgot this was why it
needed to be reverted the first time)

Original change's description:
> Roll emsdk to 4.0.20
>
> gclient setdep -r third_party/emsdk@e4fe26ef59168ff44f4c23c466e497bf60b3411e
>
> Bug: 456628846
> Change-Id: I7b7f38d409abb9f33f8bf1deef5af4523f132f58
> Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/276940
> Commit-Queue: Kai Ninomiya <kainino@chromium.org>
> Reviewed-by: Fr <beaufort.francois@gmail.com>

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 456628846
Change-Id: Ia909e151a90fa434d566a6be64f5add73e0c8d18
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/277415
Reviewed-by: Fr <beaufort.francois@gmail.com>
Commit-Queue: rubber-stamper@appspot.gserviceaccount.com <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Kai Ninomiya <kainino@chromium.org>
Bot-Commit: rubber-stamper@appspot.gserviceaccount.com <rubber-stamper@appspot.gserviceaccount.com>
diff --git a/DEPS b/DEPS
index 9245dbf..96cf946 100644
--- a/DEPS
+++ b/DEPS
@@ -382,7 +382,7 @@
   'third_party/emsdk': {
     # Note: Always use an emsdk hash referring to a tagged release, just so
     # emsdk and emscripten are always in sync with an exact release.
-    'url': '{chromium_git}/external/github.com/emscripten-core/emsdk.git@e4fe26ef59168ff44f4c23c466e497bf60b3411e',
+    'url': '{chromium_git}/external/github.com/emscripten-core/emsdk.git@eff90ca04a3785f571a8095b3a42b63799cf384a',
     'condition': 'dawn_wasm',
   },
 
diff --git a/third_party/emsdk b/third_party/emsdk
index e4fe26e..eff90ca 160000
--- a/third_party/emsdk
+++ b/third_party/emsdk
@@ -1 +1 @@
-Subproject commit e4fe26ef59168ff44f4c23c466e497bf60b3411e
+Subproject commit eff90ca04a3785f571a8095b3a42b63799cf384a