--- a/build/macosx/check-sync-exceptions
+++ b/build/macosx/check-sync-exceptions
@@ -1,4 +1,7 @@
 # Install OSX Bug 1400533
 # Until we are cross-building OSX or the OS on the build workers are updated,
 # we need to use a newer SDK than the installed SDK.
 local-mozconfig.common
+
+# Rather than trying to keep this up to date, we just error out here.
+cross-mozconfig.common

--- a/build/macosx/cross-mozconfig.common
+++ b/build/macosx/cross-mozconfig.common
@@ -1,54 +1,2 @@
-# This Source Code Form is subject to the terms of the Mozilla Public
-# License, v. 2.0. If a copy of the MPL was not distributed with this
-# file, You can obtain one at http://mozilla.org/MPL/2.0/.
-
-MOZ_AUTOMATION_L10N_CHECK=0
-
-if [ "x$IS_NIGHTLY" = "xyes" ]; then
-  # Some nightlies (eg: Mulet) don't want these set.
-  MOZ_AUTOMATION_UPDATE_PACKAGING=${MOZ_AUTOMATION_UPDATE_PACKAGING-1}
-fi
-. "$topsrcdir/build/mozconfig.common"
-
-# ld needs libLTO.so from llvm
-mk_add_options "export LD_LIBRARY_PATH=$topsrcdir/clang/lib"
-
-CROSS_CCTOOLS_PATH=$topsrcdir/cctools
-# This SDK was copied from a local XCode install and uploaded to tooltool.
-# Generate the tarball by running this command with the proper SDK version:
-#   sdk_path=$(xcrun --sdk macosx10.12 --show-sdk-path)
-#   tar -C $(dirname ${sdk_path}) -cHjf /tmp/$(basename ${sdk_path}).tar.bz2 $(basename ${sdk_path})
-# Upload the resulting tarball from /tmp to tooltool, and change the entry in
-# `browser/config/tooltool-manifests/macosx64/cross-releng.manifest`.
-CROSS_SYSROOT=$topsrcdir/MacOSX10.11.sdk
-CROSS_PRIVATE_FRAMEWORKS=$CROSS_SYSROOT/System/Library/PrivateFrameworks
-FLAGS="-target x86_64-apple-darwin11 -B $CROSS_CCTOOLS_PATH/bin -isysroot $CROSS_SYSROOT"
-
-export CC="$topsrcdir/clang/bin/clang $FLAGS"
-export CXX="$topsrcdir/clang/bin/clang++ $FLAGS"
-export CPP="$topsrcdir/clang/bin/clang $FLAGS -E"
-export LLVMCONFIG=$topsrcdir/clang/bin/llvm-config
-export LDFLAGS="-Wl,-syslibroot,$CROSS_SYSROOT -Wl,-dead_strip"
-export BINDGEN_CFLAGS="$FLAGS"
-export TOOLCHAIN_PREFIX=$CROSS_CCTOOLS_PATH/bin/x86_64-apple-darwin11-
-export DSYMUTIL=$topsrcdir/clang/bin/llvm-dsymutil
-export MKFSHFS=$topsrcdir/hfsplus-tools/newfs_hfs
-export DMG_TOOL=$topsrcdir/dmg/dmg
-export HFS_TOOL=$topsrcdir/dmg/hfsplus
-
-export HOST_CC="$topsrcdir/clang/bin/clang"
-export HOST_CXX="$topsrcdir/clang/bin/clang++"
-export HOST_CPP="$topsrcdir/clang/bin/clang -E"
-export HOST_CFLAGS="-g"
-export HOST_CXXFLAGS="-g"
-export HOST_LDFLAGS="-g"
-
-ac_add_options --target=x86_64-apple-darwin
-ac_add_options --with-macos-private-frameworks=$CROSS_PRIVATE_FRAMEWORKS
-
-if [ "x$MOZ_PKG_SPECIAL" != "xasan" -a -z "$MOZ_AUTOMATION_ARTIFACT_BUILDS" ]; then
-  # Enable static analysis checks by default on OSX cross builds.
-  # Exception is ASan, where this breaks.
-  # The option is not valid on artifact builds, so don't add it there either.
-  ac_add_options --enable-clang-plugin
-fi
+echo "cross-building with comm-central as top dir not supported"
+exit 1