modpost: Permit .GCC.command.line sections

Allow .GCC.command.line sections in modules to prevent modpost warnings:
WARNING: sound/usb/snd-usbmidi-lib.o (.GCC.command.line): unexpected non-allocatable section.
Did you forget to use "ax"/"aw" in a .S file?
Note that for example <linux/init.h> contains
section definitions for use in .S files.

Signed-off-by: Jonathan Kliegman <kliegs@chromium.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>