Bug 1584217 - Increase the timeout for the clang-aarch64 toolchain r=nalexander

With clang-8 sources, this task was already pretty close to the limit with typical times of 54-58 minutes.

In clang-9, enough new code was added that we're seeing frequent intermittent timeouts. Even the few successful builds come in just under the wire at 60 minutes.

Note for sheriffs, if the clang-9 update gets backed out, this patch can stay, we'll need it anyway.

Differential Revision: https://phabricator.services.mozilla.com/D47288

--HG--
extra : moz-landing-system : lando

taskcluster/ci/toolchain/clang.yml

@@ -136,7 +136,7 @@ linux64-clang-8-aarch64-cross:
         symbol: TL(clang8-aarch64)
     worker-type: b-linux
     worker:
-        max-run-time: 3600
+        max-run-time: 5400
         docker-image: {in-tree: toolchain-arm64-build}
     run:
         using: toolchain-script