Adapt to backwards incompatible change in GNU Make 4.3
    
    GNU Make 4.3 has a backwards incompatible change affecting the use of
    number signs or hashes (ie., #) inside function invocations. See:
    https://lists.gnu.org/archive/html/info-gnu/2020-01/msg00004.html
    
    In this case, it would expand the '\#' in the '\n\#include \"$(h)\"'
    argument to the foreach call to '\#', not '#'. This would lead to
    spurious backslashes in front of the '#include' directives in the
    generated gstmpegts-enumtypes.c file.
    
    Spotted by Ernestas Kulik.
    
    https://gitlab.freedesktop.org/gstreamer/common/-/merge_requests/4
    https://bugzilla.redhat.com/show_bug.cgi?id=1799497