Build glibc32 binary package from glibc sources as part of x86_64 build
    
    GCC for x86_64 includes 32-bit multilib support, requiring a 32-bit
    glibc to be present when GCC is built.  That 32-bit glibc cannot come
    from an i686 RPM because of limitations in Koji, so there is a hack
    including a glibc32 "source" package that actually contains binaries
    from an i686 build (and thus needs additional manual update steps).
    
    Set up glibc.spec to build a glibc32 binary package directly when
    building for x86_64, so avoiding the need for the separate glibc32
    source package.  This improvement is tracked in
    <https://fedoraproject.org/wiki/Changes/glibc32_Build_Adjustments> and
    <https://bugzilla.redhat.com/show_bug.cgi?id=1598524>.
    
    The list of files in the glibc32 package has been compared to that in
    the previous package (the gnu/lib-names-32.h header is added, as its
    previous omission appears to be a bug).  And the lists of files in the
    other packages built from glibc.spec have also been compared before
    and after this change, to make sure there aren't inappropriate changes
    to those lists.