test-file-cache.c needs #ifdef HAVE_RLIMIT_AS

[Rupert Gallagher]

test-file-cache.c:259:24: error: use of undeclared identifier 'RLIMIT_AS'
        test_assert(getrlimit(RLIMIT_AS, &rl_cur) == 0);
                              ^
test-file-cache.c:267:24: error: use of undeclared identifier 'RLIMIT_AS'
        test_assert(setrlimit(RLIMIT_AS, &rl_new) == 0);
                              ^
test-file-cache.c:270:24: error: use of undeclared identifier 'RLIMIT_AS'
        test_assert(setrlimit(RLIMIT_AS, &rl_cur) == 0);
                              ^
test-file-cache.c:276:24: error: use of undeclared identifier 'RLIMIT_AS'
        test_assert(setrlimit(RLIMIT_AS, &rl_new) == 0);
                              ^
test-file-cache.c:279:24: error: use of undeclared identifier 'RLIMIT_AS'
        test_assert(setrlimit(RLIMIT_AS, &rl_cur) == 0);
                              ^