[tlbuild] Harfbuzz 4.4.x

[Karl Berry]

    In file included from ../../../libs/harfbuzz/harfbuzz-src/src/hb.hh:473:0,
    from ../../../libs/harfbuzz/harfbuzz-src/src/hb-blob.cc:28:
    ../../../libs/harfbuzz/harfbuzz-src/src/hb-cplusplus.hh:170:13: error:
    specialization of 'template<class _Tp> struct std::hash' in different
    namespace [-fpermissive]
    struct std::hash<hb::shared_ptr<T>>

A basic search for that error message turns up several posts about it.
I can't delve into it now, but at a glance, seems like an intentional
incompatibility created by the language committee (as usual). In any
case, a known issue.

For example (there are plenty more):
https://www.programmersought.com/article/41522947014/
https://stackoverflow.com/questions/2282349/

Probably we'll have to patch our hb source one way or another? 

I suppose the other thing to try is newer compilers, but I suspect
that is not easy. --thanks, karl.