Move internal_{,v}warning to common/errors.[ch]

Move internal_{,v}warning to common/errors.[ch]

This commit moves internal_warning and internal_vwarning into
common/errors.[ch].

gdb/ChangeLog:

	* common/errors.h (internal_warning): New declaration.
	(internal_vwarning): Likewise.
	* common/errors.c (internal_warning): New function.
	* utils.h (internal_warning): Don't declare.
	(internal_vwarning): Likewise.
	* utils.c (internal_warning): Removed.

gdb/gdbserver/ChangeLog:

	* utils.c (internal_vwarning): New function.