Big Sur no longer has a libc library, so ttfautohint.memory fails #6

ttfautohint.memory does this:

    libc_path = find_library("c")
    if libc_path is None:
        raise OSError("Could not find the libc shared library")

On Big Sur there is no libc(!) I know there are efforts to fix ctypes loading on Python 3.8 and 3.9 but I'm not clear if that includes a workaround to the missing libc issue.

See fonttools/fontbakery#3107 for more context.