gdb: introduce frame_debug_printf

gdb: introduce frame_debug_printf

Introduce frame_debug_printf, to convert the "frame" debug messages to
the new system.  Replace fprint_frame with a frame_info::to_string
method that returns a string, like what was done with
frame_id::to_string.  This makes it easier to use with
frame_debug_printf.

gdb/ChangeLog:

	* frame.h (frame_debug_printf): New.
	* frame.c: Use frame_debug_printf throughout when printing frame
	debug messages.
	* amd64-windows-tdep.c: Likewise.
	* value.c: Likewise.

gdb/testsuite/ChangeLog:

	* gdb.dwarf2/dw2-reg-undefined.exp: Update regexp.

Change-Id: I3c230b0814ea81c23af3e1aca1aac8d4ba91d726