[lldb] Increase timeout in TestExitDuringExpression

200 microseconds is not enough time for any expression to execute
reliably. On linux, calling pthread_exit can result in call to dlopen,
which cannot complete in that time, particularly when running under a
debugger.

On linux, this test failed all the time, on macos, about two thirds of
runs were failing.  This patch increases the timeout to 100ms, which is
enough to get it passing reliably on linux, though I wouldn't be
surprised if an even bigger timeout would be needed for remote test
runs.