Avoid crash when "compile" expression uses cooked register

Avoid crash when "compile" expression uses cooked register

If the "compile" command is used with an expression that happens to
require a cooked register, then GDB can crash.  This patch does not
fix the bug, but at least turns the crash into an error instead.

2021-01-23  Tom Tromey  <tom@tromey.com>

	PR compile/25575
	* compile/compile-loc2c.c (note_register): New function.
	(pushf_register_address, pushf_register): Use it.