Add SymbolicConstantsMach and its test

util/mach/mach_extensions.h

 // Copyright 2014 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 21 matching lines @@
 // exception_type_t, it’s reasonable to assume that there cannot be any
 // officially-defined exception_type_t values higher than 31.
 // kMachExceptionSimulated uses a value well outside this range because it does
 // not require a corresponding mask value. Simulated exceptions are delivered to
 // the exception handler registered for EXC_CRASH exceptions using
 // EXC_MASK_CRASH.
 
 //! \brief An exception type to use for simulated exceptions.
 const exception_type_t kMachExceptionSimulated = 'CPsx';
 
+//! \brief The value for `EXC_MASK_ALL` appropriate for the operating system at
+//!     run time.
+//!
+//! The SDK’s definition of `EXC_MASK_ALL` has changed over time, with later
+//! versions containing more bits set than earlier versions. However, older
+//! kernels will reject exception masks that contain bits set that they don’t
+//! recognize. Calling this function will return a value for `EXC_MASK_ALL`
+//! appropriate for the system at run time.
+//!
+//! \note `EXC_MASK_ALL` does not include the value of `EXC_MASK_CRASH`.
+exception_mask_t ExcMaskAll();
+
 }  // namespace crashpad
 
 #endif  // CRASHPAD_UTIL_MACH_MACH_EXTENSIONS_H_