commit 9b2921bea1d5017832e1b45d1fd64220047a9802
Author: Rich Felker <dalias@aerifal.cx>
Date:   Sun Oct 20 03:27:58 2019 -0400

    adjust struct timespec definition to be time64-ready
    
    for time64 support on 32-bit archs, the kernel interfaces use a
    timespec layout padded to match the representation of a pair of 64-bit
    values, which requires endian-specific padding.
    
    use of an ordinary, non-bitfield, named member for the padding is
    undesirable because, on big endian archs, it would alter the
    interpretation of traditional (non-designated) initializers of the
    form {s,ns}, initializing the padding instead of the tv_nsec member.
    unnamed bitfield members solve this problem by not taking part in
    initialization, and were the expected solution when the kernel
    interfaces were designed. however, they also have further advantages
    which we take advantage of here:
    
    positioning of the padding could be controlled by having a
    preprocessor conditional with separate definitions of struct timespec
    for little and big endian, but whether padding should appear at all is
    a function of whether time_t is larger than long. this condition is
    not something the preprocessor can determine unless we were to define
    a new macro specifically for that purpose.
    
    by using unnamed bitfield members instead of ordinary named members,
    we can arrange for the size of the padding to collapse to zero when it
    should not be present, just by using sizeof(time_t) and sizeof(long)
    in the bitfield width expression, which can be any integer constant
    expression.