Allow death test child to bypass WER under MinGW

The mechanics of suppressing debugger trapping and Windows Error Reporting for the crashed child process in a death test are currently guarded under the `GTEST_HAS_SEH` macro. This seems unnecessary, as the logic does not call any APIs related to Structured Error Handling.

Replace the guarding macro with the more permissive `GTEST_OS_WINDOWS`, so that Windows toolchains without SEH support (e.g. MinGW) can benefit from it.

Fixes: #1116

googletest/src/gtest.cc

@@ -4214,7 +4214,7 @@ int UnitTest::Run() {
   // used for the duration of the program.
   impl()->set_catch_exceptions(GTEST_FLAG(catch_exceptions));
 
-#if GTEST_HAS_SEH
+#if GTEST_OS_WINDOWS
   // Either the user wants Google Test to catch exceptions thrown by the
   // tests or this is executing in the context of death test child
   // process. In either case the user does not want to see pop-up dialogs
@@ -4251,7 +4251,7 @@ int UnitTest::Run() {
           _WRITE_ABORT_MSG | _CALL_REPORTFAULT);  // pop-up window, core dump.
 # endif
   }
-#endif  // GTEST_HAS_SEH
+#endif  // GTEST_OS_WINDOWS
 
   return internal::HandleExceptionsInMethodIfSupported(
       impl(),