Get test executables compiling on Windows.

Many of the test executables use pthreads directly.  This isn't
portable on Windows, so this patch converts these test to use
C++11 threads and mutexes.  Since Windows' implementation of
std::thread classes throw and catch from header files, this patch
also disables exceptions when compiling with clang on Windows.

Reviewed by: Todd Fiala, Ed Maste

Differential Revision: http://reviews.llvm.org/D4816