Disable swiftcall test on windows: More brutal way to appease windows bots

The backtrace on the bot does not give me any indication what is wrong.
The test case interestingly passes in stage2 of the build.
I don't have a way of debugging this.

Disable the test on windows and hope if there is truly a bug in the code that
was causing we will eventually run into this on other platforms.

llvm-svn: 284174