Add SymbolicConstantsMach 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..d13a5851635262ef6036e4b89134bb886d08d314 100644
--- a/util/mach/mach_extensions.h
+++ b/util/mach/mach_extensions.h
@@ -39,6 +39,18 @@ const mach_port_t kMachPortNull = MACH_PORT_NULL;
 //! \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_