Add sys/file.h for LOCK_
    
    Fixes build with musl:
    | ../git/src/shared/dissect-image.c: In function 'mount_image_privately_interactively':
    | ../git/src/shared/dissect-image.c:2986:34: error: 'LOCK_SH' undeclared (first use in this function)
    |  2986 |         r = loop_device_flock(d, LOCK_SH);
    |       |                                  ^~~~~~~
    
    (cherry picked from commit 19df770fe14da601d4e54e1592c11c10ffe4df5a)