* src/hb-cff-interp-dict-common.hh: Use ull for unsigned int64_t

The llu suffix does not work for older Visual Studio versions
(pre-2013), but ull works for all the compilers that we attempt to
support.

* test/api: Fix build on pre-C99 compilers

Ensure variables are declared at the top of the block.

* src/hb-dsalgs.hh: Add specialization for hb_is_signed<> for __int8

Pre-Visual Studio 2010 does not consider __int8 (which is typedef'ed to
int8_t) to be equivilant to signed char, so the compiler cannot find the
corresponding hb_is_signed<> specialization that is needed.

The interesting thing is unsigned __int8 is considered to be equivilant
to unsigned char, so as the other types (short, int, long) that we look
for here, so only the specialization for __int8 is added here.

This will fix builds on Visual Studio 2008 at least.

https://github.com/harfbuzz/harfbuzz/issues/1496#issuecomment-448818112

Spotted it accidentally but wanted to see if is anything serious so went for fixing it

The ideas there are all part of hb-array.hh now.  To be determined how we
want to use generic iterator patterns.

I think I like to keep this hb_supplier_t thing separately from hb_array_t.

We'll see which old clang versions this breaks...

We cannot take address hb_bytes_t direction.  We need to use the
newly added hb_addressof(), ala std::addressof().

Fixes https://github.com/harfbuzz/harfbuzz/issues/1491

Not needed.  We get it in our config.h automatically thanks to
AC_USE_SYSTEM_EXTENSIONS.  Let's see whose build it breaks...
If we end up putting it back, we should add other things from
that macro and remove the macro.

Related to https://github.com/harfbuzz/harfbuzz/issues/1478

In lieu of constructor removed in previous commit.

Ouch!

Looks like operator hb_array_t<> from vector works here. :)