Merge r276128: libunwind: limit stack usage in unwind cursor

#  define _LIBUNWIND_TARGET_I386 1

#  define _LIBUNWIND_CONTEXT_SIZE 8

#  define _LIBUNWIND_CURSOR_SIZE 19

#  define _LIBUNWIND_HIGHEST_DWARF_REGISTER 9

# elif defined(__x86_64__)

#  define _LIBUNWIND_TARGET_X86_64 1

#  define _LIBUNWIND_CONTEXT_SIZE 21

#  define _LIBUNWIND_CURSOR_SIZE 33

#  define _LIBUNWIND_HIGHEST_DWARF_REGISTER 17

# elif defined(__ppc__)

#  define _LIBUNWIND_TARGET_PPC 1

#  define _LIBUNWIND_CONTEXT_SIZE 117

#  define _LIBUNWIND_CURSOR_SIZE 128

#  define _LIBUNWIND_HIGHEST_DWARF_REGISTER 113

# elif defined(__aarch64__)

#  define _LIBUNWIND_TARGET_AARCH64 1

#  define _LIBUNWIND_CONTEXT_SIZE 66

#  define _LIBUNWIND_CURSOR_SIZE 78

#  define _LIBUNWIND_HIGHEST_DWARF_REGISTER 96

# elif defined(__arm__)

#  define _LIBUNWIND_TARGET_ARM 1

#  if defined(__ARM_WMMX)

#    define _LIBUNWIND_CONTEXT_SIZE 42

#    define _LIBUNWIND_CURSOR_SIZE 49

#  endif

#  define _LIBUNWIND_HIGHEST_DWARF_REGISTER 96

# elif defined(__or1k__)

#  define _LIBUNWIND_TARGET_OR1K 1

#  define _LIBUNWIND_CONTEXT_SIZE 16

#  define _LIBUNWIND_CURSOR_SIZE 28

#  define _LIBUNWIND_HIGHEST_DWARF_REGISTER 32

# else

#  error "Unsupported architecture."

# endif

# define _LIBUNWIND_TARGET_OR1K 1

# define _LIBUNWIND_CONTEXT_SIZE 128

# define _LIBUNWIND_CURSOR_SIZE 140

# define _LIBUNWIND_HIGHEST_DWARF_REGISTER 120

#endif // _LIBUNWIND_IS_NATIVE_ONLY

#endif // ____LIBUNWIND_CONFIG_H__

  };

  enum {

    kMaxRegisterNumber = 120

    kMaxRegisterNumber = _LIBUNWIND_HIGHEST_DWARF_REGISTER

  };

  enum RegisterSavedWhere {

    kRegisterUnused,