Add run-pass-valgrind tests

[nrc]

I would like some rpass to always be run under Valgrind. These are mostly cleanup tests, to check that all memory is freed and we don't double free memory.

I propose adding a directory to tests - run-pass-valgrind. Any tests inside are treated like run-pass tests, but on systems with Valgrind (which should include the bots with every push) all tests are run under Valgrind (maybe as well as without Valgrind, or maybe just with Valgrind, not sure if there is benefit to running without). The test fails if it fails to compile, a task fails (as with regular run-pass tests), or there are any Valgrind errors. On systems without Valgrind, they should be run like the regular run-pass tests.