Run single subtest from a test file

[gctony]

Add mechanism to be able to select one or more tests to run from a test file. The test harness will read JEMALLOC_TEST_REGEX env and, if set, compile it as a regex. It will then only run tests whose name match the regex.

[gctony]

Unfortunately, windows is not happy with regex.h. I don't want to spend too much time on this, I'll just remove the regex feature and only allow a single test to be chosen.

[gctony]

Example usage:

default behavior:

> bash ./test/test.sh test/unit/hpa
=== test/unit/hpa ===
test_alloc_max (non-reentrant): pass
test_stress (non-reentrant): pass
test_defer_time (non-reentrant): pass
test_purge_no_infinite_loop (non-reentrant): pass
test_no_min_purge_interval (non-reentrant): pass
test_min_purge_interval (non-reentrant): pass
test_purge (non-reentrant): pass
test_experimental_max_purge_nhp (non-reentrant): pass
test_vectorized_opt_eq_zero (non-reentrant): pass
test_starts_huge (non-reentrant): pass
test_start_huge_purge_empty_only (non-reentrant): pass
test_assume_huge_purge_fully (non-reentrant): pass
test_eager_with_purge_threshold (non-reentrant): pass
test_delay_when_not_allowed_deferral (non-reentrant): pass
test_deferred_until_time (non-reentrant): pass
test_eager_no_hugify_on_threshold (non-reentrant): pass
test_hpa_hugify_style_none_huge_no_syscall (non-reentrant): pass
test_experimental_hpa_enforce_hugify (non-reentrant): pass
--- pass: 18/18, skip: 0/18, fail: 0/18 ---

Test suite summary: pass: 1/1, skip: 0/1, fail: 0/1

select one test:

> JEMALLOC_TEST_NAME=test_stress bash ./test/test.sh test/unit/hpa
=== test/unit/hpa ===
test_stress (non-reentrant): pass
--- pass: 1/1, skip: 0/1, fail: 0/1 ---

Test suite summary: pass: 1/1, skip: 0/1, fail: 0/1