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

[Karl Berry]

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 suppose it is some C++ feature that is not supported. Anyone
up for researching if there's so`lme way we can tweak the source to make
it work? I won't have time to look at it for a couple of
days. --thanks, karl.

[...]
g++ -std=gnu++11 -DHAVE_CONFIG_H -I. -I../../../libs/harfbuzz  -DHB_NO_MT -DHAVE_FALLBACK=1 -I../../../libs/harfbuzz/harfbuzz-src/src -I/home/texlive/karl/Build/source/Work/libs/graphite2/include -DGRAPHITE2_STATIC   -g  -fno-rtti -fno-exceptions -Wcast-align -MT harfbuzz-src/src/hb-face.o -MD -MP -MF $depbase.Tpo -c -o harfbuzz-src/src/hb-face.o ../../../libs/harfbuzz/harfbuzz-src/src/hb-face.cc &&\
mv -f $depbase.Tpo $depbase.Po
In file included from ../../../libs/harfbuzz/harfbuzz-src/src/hb.hh:651:0,
                 from ../../../libs/harfbuzz/harfbuzz-src/src/hb-face.cc:29:
../../../libs/harfbuzz/harfbuzz-src/src/hb-algs.hh: In instantiation of 'decltype (hb_partial<2>(this, hb_forward<_T>(_v)))<anonymous struct>::operator()(_T&&) const [with _T = const OT::cmap* const; decltype (hb_partial<2>(this, hb_forward<_T>(_v))) = hb_partial_t<2u, const<anonymous struct>* const&, const OT::cmap* const>]':
../../../libs/harfbuzz/harfbuzz-src/src/hb-ot-cmap-table.hh:1167:27:   required from here
../../../libs/harfbuzz/harfbuzz-src/src/hb-meta.hh:68:56: error: could not convert 'hb_partial<2u, const<anonymous struct>* const, const OT::cmap* const>((* & this), (* & hb_forward<const OT::cmap* const>((* & _v))))' from 'hb_partial_t<2u, const<anonymous struct>* const, const OT::cmap* const>' to 'hb_partial_t<2u, const<anonymous struct>* const&, const OT::cmap* const>'
 #define HB_AUTO_RETURN(E) -> decltype ((E)) { return (E); }
                                                        ^
../../../libs/harfbuzz/harfbuzz-src/src/hb-algs.hh:172:36: note: in expansion of macro 'HB_AUTO_RETURN'
   auto operator () (_T&& _v) const HB_AUTO_RETURN (hb_partial<Pos> (this, hb_forward<_T> (_v))) \
                                    ^
../../../libs/harfbuzz/harfbuzz-src/src/hb-algs.hh:839:3: note: in expansion of macro 'HB_PARTIALIZE'
 { HB_PARTIALIZE(2);
   ^
make[4]: *** [Makefile:1203: harfbuzz-src/src/hb-face.o] Error 1
make[4]: Leaving directory '/home/texlive/karl/Build/source/Work/libs/harfbuzz'