exception handler ports.
task_t, thread_t, and exception_handler_t are typedefs for mach_port_t.
They are more descriptive than mach_port_t, and are already in use in
exc_server_variants.
TEST=util_test
R=rsesek@chromium.org
Review URL: https://codereview.chromium.org/577293002
This also puts kMachExceptionCodes into mach_extensions.h, because a
form of MACH_EXCEPTION_CODES that’s the right type
(exception_behavior_t) has now shown its use in more than one file.
TEST=util_test ExcClientVariants.UniversalExceptionRaise
R=rsesek@chromium.org
Review URL: https://codereview.chromium.org/567283002
