Added clang-tidy-target-cmake support.

By default all checked targets will be checked with clang-tidy,
the llvm-* and google-* checks excluded.

Use CLANG_TIDY_ENABLE_CHECK and CLANG_TIDY_DISABLE_CHECKS on each
checked target to enable or disable particular checks.

POLYSQUARE_USE_CLANG_TIDY can be set to OFF to disable clang-tidy
for a particular build.