Use make_formatted_string to avoid double length calculation.

Use make_formatted_string to avoid double length calculation.
* lisp.h (make_formatted_string): New prototype.
* alloc.c (make_formatted_string): New function.
* buffer.c (Fgenerate_new_buffer_name): Use it.
* dbus.c (syms_of_dbusbind): Likewise.
* editfns.c (Fcurrent_time_zone): Likewise.
* filelock.c (get_boot_time): Likewise.
* frame.c (make_terminal_frame, set_term_frame_name)
(x_report_frame_params): Likewise.
* image.c (gs_load): Likewise.
* minibuf.c (get_minibuffer): Likewise.
* msdos.c (dos_set_window_size): Likewise.
* process.c (make_process): Likewise.
* xdisp.c (ensure_echo_area_buffers): Likewise.
* xsettings.c (apply_xft_settings): Likewise.