[Bug testsuite/81920] Improve timing-sensitive libgomp.oacc testcases

["vries at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81920

--- Comment #1 from Tom de Vries <vries at gcc dot gnu.org> ---
Created attachment 42026
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42026&action=edit
tentative patch for lib-81.c

The only problem: error reporting has not improved a lot.

When I hand-edit the test-case to make the matching fail:
...
- /* { dg-output ".*actual time 3 < 0.10: ok"  } */
+ /* { dg-output ".*actual time 3 < 0.11: ok"  } */
...

We just get:
...
FAIL: libgomp.oacc-c/../libgomp.oacc-c-c++-common/lib-81.c
-DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0  -O2  output pattern test
...
so, no line saying: this individual dg-output line failed.

In libgomp.log, things are not too readable either:
...
FAIL: libgomp.oacc-c/../libgomp.oacc-c-c++-common/lib-81.c
-DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0  -O2  output pattern test
Output was:
actual time 1: 528.946960, delay time: 500.000000
actual time 1 >= delay time: ok
actual time 2: 0.073856
actual time 2 < 0.10: ok
actual time 3: 0.022368
actual time 3 < 0.10: ok

Should match:
actual time 1 >= delay time: ok.*actual time 2 < 0.10: ok.*actual time 3 <
0.11: ok
...