Put all XSAN bots on the same DEPS-sourced build of Clang.

tools/xsan_build

 #!/bin/bash
 
 # Build Skia with one of Clang's many sanitizers.
 #
 # $ tools/xsan_build {address,thread,undefined,etc.} [any other flags to pass to make...]
 #
 # This script assumes the use of Clang >=3.2.
 #
 # For more information, see:
 #   http://clang.llvm.org/docs/UsersManual.html#controlling-code-generation
 
 set -e
 set -x
 
-export CC=clang
-export CXX=clang++
+here=$(cd `dirname $0`; echo `pwd`)
+cores=48
+
+echo "Bootstrapping CMake"
+pushd $here/../third_party/externals/cmake
+./bootstrap --parallel=$cores
+make -j $cores cmake
+popd
+
+echo "Building Clang"
+pushd $here/../third_party/externals/llvm
+mkdir -p out/
+cd out/
+$here/../third_party/externals/cmake/bin/cmake -DCMAKE_BUILD_TYPE=Release -G Ninja ..
+ninja
+popd
+
+export CC=$here/../third_party/externals/llvm/out/bin/clang
+export CXX=$here/../third_party/externals/llvm/out/bin/clang++
 $CC --version
 
 if [[ "$1" == "memory" ]]; then
     export GYP_DEFINES="skia_gpu=0 skia_no_fontconfig=1 skia_freetype_static=1 ${GYP_DEFINES}"
 fi
 export GYP_DEFINES="skia_sanitizer=$1 ${GYP_DEFINES}"
 
 shift
 make $@