[tlbuild] Harfbuzz 4.4.x

[Mojca Miklavec]

Hi,

the upgrade to harfbuzz 4.4.0
    https://tug.org/svn/texlive?view=revision&revision=63743
seems to have broken the builds on Solaris 10 (gcc 5.5) and Debian 9 (gcc 6.3).

I'm NOT proposing to revert the upgrade, but we might want to figure
out how to address the issue.

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>>
^~~~~~~~~~~~~~~~~~~~~~~

Mojca