Make the C tests work with the --enable-optimize configure option.
Because the main() function used to be defined in libsvn_test, the -flto option (which performs rather aggressive link-time optimizations) would cause the linker to remove all "unreferenced" static functions ... which includes all the actual tests.
Which this change, main() is now defined in each test driver.
* subversion/tests/svn_test.h (test_funcs, svn_test_max_threads): Remove external declarations. (svn_test_main): New prototype for the (existing-but-renamed) test driver. (SVN_TEST_MAIN): Bolierplate macro that generates a main() implementation.
* subversion/tests/svn_test_main.c (svn_test_main): Renamed from 'main', and takes two extra parameters, 'max_threads' and 'test_funcs'. Propagates test_funcs to get_array_size, do_test_num and do_tests_concurrently. (get_array_size, do_test_num, test_params_t, test_thread, do_tests_concurrently): Require a test_funcs parameter. All uses updated.