message: getdeps: add support for using ccache in cmake builds
  Summary:
  if we find ccache in the path, then we instruct cmake to use
  it as the compiler launcher.
diff: @@ -229,6 +229,9 @@ class CMakeBuilder(BuilderBase):
  "CMAKE_BUILD_TYPE": "RelWithDebInfo",
  }
  env = self._compute_env(install_dirs)
  + ccache = path_search(env, "ccache")
  + if ccache:
  + defines["CMAKE_CXX_COMPILER_LAUNCHER"] = ccache
  if self.build_opts.is_darwin():
  # Try to persuade cmake to set the rpath to match the lib
  # dirs of the dependencies. This isn't automatic, and to
  