scons: Tell MSVC STL library to not use exceptions.

MSVC defaults to no exceptions unless /EH option is passed (which we don't), while
MSVC's STL defaults to use exceptions unless _HAS_EXCEPTIONS=0 is defined,
which we didn't.

This fixes

  warning C4530: C++ exception handler used, but unwind semantics are not enabled. Specify /EHsc

Reviewed-by: Brian Paul <brianp@vmware.com>
1 file changed