PATCH [2/n]: Add x32 sysdep.h file

[Roland McGrath]

This again has unrelated things in one patch, unrelated things in one log
paragraph, and related things in separate log paragraphs.  It's all wrong.

The moving of VSYSCALL_ADDR_* is all one change: one patch, one paragraph.

The PTR_{,DE}MANGLE change is its own change: one patch, one paragraph.

The pure CPU changes are separate from the OS-specific ones.
e.g. the new sysdeps/x86_64/sysdep.h macros and the addition of
sysdeps/x86_64/x32/sysdep.h is one change.  But the addition
ofsysdeps/unix/sysv/linux/x86_64/x32/sysdep.h is a separate change.

Say "New file" or "New macro" or "New function" or whatever, not just "New".


Thanks,
Roland