bpo-30764: Windows support.SuppressCrashReport (#2423)

* Add Windows support to test.support.SuppressCrashReport: call
  SetErrorMode() and CrtSetReportMode().
* _testcapi: add CrtSetReportMode() and CrtSetReportFile() functions
  and CRT_xxx and CRTDBG_xxx constants needed by SuppressCrashReport.
2 files changed