Adding Google benchmarking library.

third_party/google_benchmark/.travis-libcxx-setup.sh

Index: third_party/google_benchmark/.travis-libcxx-setup.sh
diff --git a/third_party/google_benchmark/.travis-libcxx-setup.sh b/third_party/google_benchmark/.travis-libcxx-setup.sh
new file mode 100644
index 0000000000000000000000000000000000000000..a591743c6a6ba93566c21eb1bbe17ab5cee08b7a
--- /dev/null
+++ b/third_party/google_benchmark/.travis-libcxx-setup.sh
@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+
+# Install a newer CMake version
+curl -sSL https://cmake.org/files/v3.6/cmake-3.6.1-Linux-x86_64.sh -o install-cmake.sh
+chmod +x install-cmake.sh
+sudo ./install-cmake.sh --prefix=/usr/local --skip-license
+
+# Checkout LLVM sources
+git clone --depth=1 https://github.com/llvm-mirror/llvm.git llvm-source
+git clone --depth=1 https://github.com/llvm-mirror/libcxx.git llvm-source/projects/libcxx
+git clone --depth=1 https://github.com/llvm-mirror/libcxxabi.git llvm-source/projects/libcxxabi
+
+# Setup libc++ options
+if [ -z "$BUILD_32_BITS" ]; then
+  export BUILD_32_BITS=OFF && echo disabling 32 bit build
+fi
+
+# Build and install libc++ (Use unstable ABI for better sanitizer coverage)
+mkdir llvm-build && cd llvm-build
+cmake -DCMAKE_C_COMPILER=${C_COMPILER} -DCMAKE_CXX_COMPILER=${COMPILER} \
+      -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_INSTALL_PREFIX=/usr \
+      -DLIBCXX_ABI_UNSTABLE=ON \
+      -DLLVM_USE_SANITIZER=${LIBCXX_SANITIZER} \
+      -DLLVM_BUILD_32_BITS=${BUILD_32_BITS} \
+      ../llvm-source
+make cxx -j2
+sudo make install-cxxabi install-cxx
+cd ../