Phobos has recently gotten a primitive way to run betterC tests
(https://github.com/dlang/phobos/pull/6640).
Now, it would be really cool if we can annotate existing tests
with e.g. `@betterCTest` and thus ensure that those tests work
with -betterC (i.e. extract them and run them with a minimal test
runner.
a) @betterC
Probably too popular and would lead to too many conflicts.
b) @TestBetterC
c) @betterCTest || @bettercTest
Would probably be defined a enum somewhere in `std.internal`
d) @("betterC")
A bit ugly and harder to work with. If we ever want to name the
unittests in Phobos, this will make it harder.
At some point we might also want to test whether something runs
even without any runtime
(https://github.com/dlang/phobos/pull/6641), so e.g.
`@baremetalTest` might be defined too.
My favorite is (c) - any objections?
See also: https://github.com/dlang/tools/pull/357 (implementation
of the test extraction filter for UDAs)
