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This patch adds the CMakeLists.txt necessary to build clang tools using
CMake. The build files have also been refactored by creating a
top-level CMakeLists.txt. The list of tools to be built can be
controlled by setting ${CHROMIUM_TOOLS}. Tools are now installed with
a CMake rule rather than a manual cp, which should make this logic a
little more platform independent.

R=hans@chromium.org

Review URL: https://codereview.chromium.org/583143002

Cr-Commit-Position: refs/heads/master@{#296081}