Unit tests in C++

The goal is to make the spec tests pass, but unit tests are helpful too.

cpp/core_test.cc                                417
cpp/data_lang_test.cc                           178
cpp/data_race_test.cc                           206
cpp/frontend_flag_spec_test.cc                  154
cpp/frontend_match_test.cc                       87
cpp/libc_test.cc                                403
cpp/obj_layout_test.cc                          214
cpp/osh_test.cc                                  50
cpp/pylib_test.cc                                52
cpp/stdlib_test.cc                              158
cpp/unicode_test.cc                              71
mycpp/bump_leak_heap_test.cc                     62
mycpp/float_test.cc                             150
mycpp/gc_builtins_test.cc                       447
mycpp/gc_dict_test.cc                           745
mycpp/gc_heap_test.cc                           479
mycpp/gc_list_test.cc                           508
mycpp/gc_mops_test.cc                           128
mycpp/gc_mylib_test.cc                          327
mycpp/gc_str_test.cc                          1,558
mycpp/gc_stress_test.cc                         222
mycpp/gc_tuple_test.cc                          139
mycpp/mark_sweep_heap_test.cc                   370
mycpp/small_str_test.cc                         502

7,627 lines in 25 files