b77cec05c0 fixed this problem for tagging tests, so that a test
case tagged with `[.foo]` would be parsed as tagged with `[.][foo]`.
This does the same for the test spec parsing.
Fixes#1798
Now that Catch2 is a proper library, we can always build the full
library (comparatively minor slowdown) and the user can avoid
including benchmarking headers to avoid the compilation slowdown.
