Fixes bug #55. A number of tests were crashing on Windows due to the task
launch code using alloca to allocate space for the tasks' parameters. On
Windows, the stack isn't generally big enough for this to be a good idea.
Also added an alignment parmaeter to ISPCMalloc() to pass the alignment
requirement along.
Link the appropriate clang libraries to make the preprocessor
stuff work on Windows builds. Also updated the solution files
for the examples to stop using cl.exe for preprocessing but to
just call ispc directly. Finishes fixes for issue #32.
