gdb: convert auto-load to new-style debug macros

gdb: convert auto-load to new-style debug macros

Function file_is_auto_load_safe was taking a format string and varargs
just to output a debug print.  This is probably because that function is
used in linux-thread-db.c and main.c, but debug_auto_load is static in
auto-load.c.  I simplified that, making debug_auto_load visible outside
of auto-load.c, and making the callers of file_is_auto_load_safe output
the debug print themselves.

This file uses _() for internationalization of the debug messages.  This
is not necessary, as these are mostly messages for GDB developers, and
it's not used in other files anyway.  So I removed them.

The rest is pretty much standard.

gdb/ChangeLog:

	* auto-load.h (debug_auto_load): Move here.
	(auto_load_debug_printf): New.
	* auto-load.c: Use auto_load_debug_printf.
	(debug_auto_load): Move to header.
	* linux-thread-db.c (try_thread_db_load): Use
	auto_load_debug_printf.
	* main.c (captured_main_1): Likewise.

Change-Id: I468dc2a1d24b7dbf171f55181a11abbfafe70ba1