Used TEST_CONSTEXPR on the merge and rotate_copy tests.
Jul 23 2020
Decomposed asserts in tests
Applied constexpr testing conventions suggested by @zoecarver.
Jul 22 2020
The builds are failing with this line standing out
ld.lld: error: unable to find library -lcxxabi_shared
Passed tests and made one internal function constexpr
Removed parts covered in https://reviews.llvm.org/D65721 and uncommented a test.