`gcc` sanitizer does not work on some environment (namely my localhost).
Although it works on Travis, it is not convenient that tests fail on the
local host. We keep sanitizer tests on the local (using `clang`).
This reverts commit 9cde967321.
The `debug` build target (`MRB_GC_STRESS` is enabled) on CI have been
compiled but not tested so far. However, I think testing with
`MRB_GC_STRESS` is effective (in fact, I found #4907 bug).
Therefore, I integrated `debug` and `full-debug` build targets to enable
`MRB_GC_STRESS` testing. Testing with `MRB_GC_STRESS` takes a little time,
but compiling takes more time, so CI execution time does not increase due to
decrease of build target.
This allows us to add `enable_test` anywhere in a build target,
without having to worry about the order in which they are included.
Previously, there was a bug that occured when adding 'mruby-test' gem
to dependencies before additional gems.
Instead of adding the 'mruby-test' gem dependency manually to a test build,
we now only need to call `enable_test` in the target. This also allows us to
call `test_enabled?` downstream when running mruby tests ourselves.
/cc #2924
KOBAYASHI Shuji