Update CTestCustom.cmake.in

Exclude "threads" test from valgrind targets
[skip ci]
Update .travis.windows.yml

change OS to Windows from Linux.
[skip ci]
Moved kernel exception formatting to kernel_exception_formatter.cpp.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Clean elaborator_exception pretty printing

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Clean elaborator_exception pretty printing