Bug 1248890 - Enable rust for win64 beta and release builds. r=rail

We've let this ride the trains for other archs. Should do so
for win64 as well.

MozReview-Commit-ID: D7dS9femsBj

browser/config/mozconfigs/whitelist

@@ -65,7 +65,6 @@ whitelist['nightly']['win32'] += [
 whitelist['nightly']['win64'] += [
     '. "$topsrcdir/browser/config/mozconfigs/win64/common-win64"',
     '. "$topsrcdir/build/mozconfig.cache"',
-    '. "$topsrcdir/build/mozconfig.rust"',
 ]
 
 for platform in all_platforms:

browser/config/mozconfigs/win64/beta

@@ -14,4 +14,6 @@ mk_add_options MOZ_PGO=1
 ac_add_options --enable-official-branding
 ac_add_options --enable-verify-mar
 
+. "$topsrcdir/build/mozconfig.rust"
+
 . "$topsrcdir/build/mozconfig.common.override"

browser/config/mozconfigs/win64/release

@@ -20,4 +20,6 @@ ac_add_options --enable-verify-mar
 # defines.sh during the beta cycle
 export BUILDING_RELEASE=1
 
+. "$topsrcdir/build/mozconfig.rust"
+
 . "$topsrcdir/build/mozconfig.common.override"