base: Mark CPUTime001 as fragile

As noted in #16224, CPUTime001 has been quite problematic, reporting
non-monotonic timestamps in CI. Unfortunately I've been unable to
reproduce this locally.

libraries/base/tests/all.T

@@ -20,7 +20,7 @@ test('tempfiles', normal, compile_and_run, [''])
 test('fixed', normal, compile_and_run, [''])
 test('quotOverflow', normal, compile_and_run, [''])
 test('assert', exit_code(1), compile_and_run, ['-fno-ignore-asserts'])
-test('CPUTime001', normal, compile_and_run, [''])
+test('CPUTime001', fragile(16224), compile_and_run, [''])
 test('readLitChar',   normal, compile_and_run, [''])
 test('unicode001',
      when(platform('i386-unknown-openbsd'), expect_fail),