Add ConstThreadState to mach_extensions.h and use it everywhere

util/mach/exc_client_variants.h

Index: util/mach/exc_client_variants.h
diff --git a/util/mach/exc_client_variants.h b/util/mach/exc_client_variants.h
index f797f448d77edc5d86e9e918d6916db073ace324..d96e689ea23f9f7784d097b239f2f26f46ee64c9 100644
--- a/util/mach/exc_client_variants.h
+++ b/util/mach/exc_client_variants.h
@@ -17,6 +17,8 @@
 
 #include <mach/mach.h>
 
+#include "util/mach/mach_extensions.h"
+
 namespace crashpad {
 
 //! \brief Calls the appropriate `*exception_raise*()` function for the
@@ -73,7 +75,7 @@ kern_return_t UniversalExceptionRaise(exception_behavior_t behavior,
                                       const mach_exception_data_type_t* code,
                                       mach_msg_type_number_t code_count,
                                       thread_state_flavor_t* flavor,
-                                      const natural_t* old_state,
+                                      ConstThreadState old_state,
                                       mach_msg_type_number_t old_state_count,
                                       thread_state_t new_state,
                                       mach_msg_type_number_t* new_state_count);