tests/stdlib/tfdleak.nim is flaky

[timotheecour]

=> nim-lang#14090

[timotheecour]

again:

https://dev.azure.com/nim-lang/255dfe86-e590-40bb-a8a2-3c0295ebdeb1/_apis/build/builds/5564/logs/66

020-05-26T00:57:50.3207683Z FAIL: tests/stdlib/tfdleak.nim C
2020-05-26T00:57:50.4589652Z Test "tests\stdlib\tfdleak.nim" in category "stdlib"
2020-05-26T00:57:50.5743175Z Failure: reOutputsDiffer
2020-05-26T00:57:50.6027572Z Expected:
2020-05-26T00:57:50.6028948Z 
2020-05-26T00:57:51.5130279Z 
2020-05-26T00:57:52.0685790Z Gotten:
2020-05-26T00:57:52.2000431Z leaked memfiles.open().fHandle
2020-05-26T00:57:52.4721272Z leaked createAsyncNativeSocket()
2020-05-26T00:57:52.8408132Z 
2020-05-26T00:57:53.0160241Z PASS: tests/stdlib/tfdleak.nim C                                   (25.76 sec)

[timotheecour]

and again https://dev.azure.com/nim-lang/255dfe86-e590-40bb-a8a2-3c0295ebdeb1/_apis/build/builds/5607/logs/66 from nim-lang#14477

2020-05-28T04:52:16.7005569Z PASS: tests/stdlib/tdecls.nim C                                    ( 5.22 sec)
2020-05-28T04:52:16.7007929Z FAIL: tests/stdlib/tfdleak.nim C
2020-05-28T04:52:16.7009528Z Test "tests\stdlib\tfdleak.nim" in category "stdlib"
2020-05-28T04:52:16.7011878Z Failure: reOutputsDiffer
2020-05-28T04:52:16.7012568Z Expected:
2020-05-28T04:52:16.7012969Z 
2020-05-28T04:52:16.7013330Z 
2020-05-28T04:52:16.7013847Z Gotten:
2020-05-28T04:52:16.7015666Z leaked accept()
2020-05-28T04:52:16.7016395Z leaked memfiles.open().fHandle
2020-05-28T04:52:16.7016854Z 
2020-05-28T04:52:16.7017795Z PASS: tests/stdlib/tfdleak.nim C                                   (23.53 sec)

[timotheecour]

2020-05-28T07:53:32.7873296Z FAIL: tests/stdlib/tfdleak.nim C
2020-05-28T07:53:33.6066806Z Test "tests\stdlib\tfdleak.nim" in category "stdlib"
2020-05-28T07:53:33.6903798Z Failure: reOutputsDiffer
2020-05-28T07:53:33.9014603Z Expected:
2020-05-28T07:53:33.9680608Z 
2020-05-28T07:53:34.6068875Z 
2020-05-28T07:53:34.9161680Z Gotten:
2020-05-28T07:53:34.9792686Z leaked accept()
2020-05-28T07:53:35.2134602Z 
2020-05-28T07:53:35.5764122Z PASS: tests/stdlib/tfdleak.nim C                                   (26.91 sec)