* Try to build on Ubuntu-18.04 with Clang-9
* Build with pushes on clang-9 branch too
* Using CC and CXX to set clang-9
* Adding atomic lib for test build on Linux with Clang
* Partial conversion CHECK_EQUAL to CHECK for clang-9
* Replaced CHECK_EQUAL with CHECK
* Replaced CHECK_EQUAL with CHECK
* Replaced CHECK_EQUAL with CHECK
* Replaced CHECK_EQUAL with CHECK
* Replaced CHECK_EQUAL with CHECK
* Replaced CHECK_EQUAL with CHECK
* Replaced CHECK_EQUAL with CHECK
Co-authored-by: finger42 <finger42>
* Enable span tests
* Handle dynamic extent in span::subspan
Fixes#234
Correct handling when count equals dynamic_extent,
which would previously cause the end pointer to be set to the
wrong location.
