Check out clang from $LLVM_URL if it's set.

tools/clang/scripts/update.sh

 #!/bin/bash
 # Copyright (c) 2011 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # This script will check out llvm and clang into third_party/llvm and build it.
 
 THIS_DIR="$(dirname "${0}")"
 LLVM_DIR="${THIS_DIR}"/../../../third_party/llvm
 CLANG_DIR="${LLVM_DIR}"/tools/clang
 DEPS_FILE="${THIS_DIR}"/../../../DEPS
 
+# ${A:-a} returns $A if it's set, a else.
+LLVM_REPO_URL=${LLVM_URL:-http://llvm.org/svn/llvm-project}
+
 # Die if any command dies.
 set -e
 
 # Since people need to run this script anyway to compile clang, let it check out
 # clang as well if it's not in DEPS, so that people don't have to change their
 # DEPS if they just want to give clang a try.
 CLANG_REVISION=$(grep 'clang_revision":' "${DEPS_FILE}" | egrep -o [[:digit:]]+)
 
 if grep -q 'src/third_party/llvm":' "${DEPS_FILE}"; then
   echo LLVM pulled in through DEPS, skipping LLVM update step
 else
   echo Getting LLVM r"${CLANG_REVISION}" in "${LLVM_DIR}"
-  svn co --force \
-    http://llvm.org/svn/llvm-project/llvm/trunk@"${CLANG_REVISION}" \
-    "${LLVM_DIR}"
+  svn co --force "${LLVM_REPO_URL}"/llvm/trunk@"${CLANG_REVISION}" "${LLVM_DIR}"
 fi
 
 if grep -q 'src/third_party/llvm/tools/clang":' "${DEPS_FILE}"; then
   echo clang pulled in through DEPS, skipping clang update step
 else
   echo Getting clang r"${CLANG_REVISION}" in "${CLANG_DIR}"
-  svn co --force \
-    http://llvm.org/svn/llvm-project/cfe/trunk@"${CLANG_REVISION}" \
-    "${CLANG_DIR}"
+  svn co --force "${LLVM_REPO_URL}"/cfe/trunk@"${CLANG_REVISION}" "${CLANG_DIR}"
 fi
 
 # Echo all commands.
 set -x
 
 # Build clang (in a separate directory).
 # The clang bots have this path hardcoded in built/scripts/slave/compile.py,
 # so if you change it you also need to change these links.
 mkdir -p "${LLVM_DIR}"/../llvm-build
 cd "${LLVM_DIR}"/../llvm-build
@@ skipping 15 matching lines @@
 # plugin.
 PLUGIN_SRC_DIR="${THIS_DIR}"/../plugins
 PLUGIN_DST_DIR="${LLVM_DIR}"/../llvm/tools/clang/tools/chrome-plugin
 PLUGIN_BUILD_DIR="${LLVM_DIR}"/../llvm-build/tools/clang/tools/chrome-plugin
 rm -rf "${PLUGIN_DST_DIR}"
 cp -R "${PLUGIN_SRC_DIR}" "${PLUGIN_DST_DIR}"
 rm -rf "${PLUGIN_BUILD_DIR}"
 mkdir -p "${PLUGIN_BUILD_DIR}"
 cp "${PLUGIN_SRC_DIR}"/Makefile "${PLUGIN_BUILD_DIR}"
 make -j"${NUM_JOBS}" -C "${PLUGIN_BUILD_DIR}"