[clang] Bump minimum Android API level to 21

A new NDK release is dropping support for API levels 19/20.

Bug: 1509859
Change-Id: Ica0cdc2e8616c5ab8101890d436515673a50c1f9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5133000
Commit-Queue: Arthur Eubanks <aeubanks@google.com>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1240355}
NOKEYCHECK=True
GitOrigin-RevId: 7e970585fb50bfbb27befe11056d0490b34f1721
diff --git a/update_rust.py b/update_rust.py
index b92195e..ac60e83 100755
--- a/update_rust.py
+++ b/update_rust.py
@@ -35,7 +35,7 @@
 # this back to its previous value _AND_ set `OVERRIDE_CLANG_REVISION` below
 # to the `CLANG_REVISION` that was in place before the roll.
 RUST_REVISION = 'df0295f07175acc7325ce3ca4152eb05752af1f2'
-RUST_SUB_REVISION = 3
+RUST_SUB_REVISION = 4
 
 # If not None, this overrides the `CLANG_REVISION` in
 # //tools/clang/scripts/update.py in order to download a Rust toolchain that