[tlbuild] more c++ agony, now with harfbuzz

[Akira Kakuto]

Hi Karl,

> Harfbuzz 2.5.0 fails to compile with the centos7-provided compiler
> (which can compile everything else, including the parts that require
> C++11).

I have imported harfbuzz-2.5.2.
Developers say that it supports gcc 4.8 again. Please test.

Thanks,
Akira