Bug 1527463 - Get full artifact build symbols for aarch64 EME builds. r=mshal

We need to have full symbols uploaded for the upcoming EME-enabled
win64-aarch64 nightlies, and the tasks to do that are derived from the
nightly itself, which is going to be an artifact build. Bug 1527463 took
care of adding the option to enable that, and we turn it on for
EME-enabled builds.

MOZ_ARTIFACT_TASK_WIN32_OPT is not exactly the right thing, but we're
already using it to enable EME in
browser/config/mozconfigs/win64-aarch64/common-opt and is only set on
those builds.

Differential Revision: https://phabricator.services.mozilla.com/D23639

build/mozconfig.artifact

@@ -2,6 +2,10 @@
 
 # Enable the artifact build.
 ac_add_options --enable-artifact-builds
-ac_add_options --enable-artifact-build-symbols
+if test -n "$MOZ_ARTIFACT_TASK_WIN32_OPT"; then
+  ac_add_options --enable-artifact-build-symbols=full
+else
+  ac_add_options --enable-artifact-build-symbols
+fi
 
 . "$topsrcdir/build/mozconfig.no-compile"