Add exc_client_variants (UniversalRaiseException()) and its test

util/mach/mach_extensions.h

Index: util/mach/mach_extensions.h
diff --git a/util/mach/mach_extensions.h b/util/mach/mach_extensions.h
index 81e9a86a97f6f72b486f53606e3d594827010696..deb1501cfe17403cb983b5da56fda02ad43e422e 100644
--- a/util/mach/mach_extensions.h
+++ b/util/mach/mach_extensions.h
@@ -28,6 +28,14 @@ namespace crashpad {
 //! assertions.
 const mach_port_t kMachPortNull = MACH_PORT_NULL;
 
+//! \brief `MACH_EXCEPTION_CODES` with the correct type for a Mach exception
+//!     behavior, `exception_behavior_t`.
+//!
+//! Signedness problems can occur when ORing `MACH_EXCEPTION_CODES` as a signed
+//! integer, because a signed integer overflow results. This constant can be
+//! used instead of `MACH_EXCEPTION_CODES` in such cases.
+const exception_behavior_t kMachExceptionCodes = MACH_EXCEPTION_CODES;
+
 // Because exception_mask_t is an int and has one bit for each defined
 // exception_type_t, it’s reasonable to assume that there cannot be any
 // officially-defined exception_type_t values higher than 31.