That's better use of that value than requiring extra macro HB_NO_ATEXIT

Fixes #1235.

Cygwin is a Posix platform to the extent possible.  It should use the
Posix API except in special circumstances.

Disable copy/assign on them, as they shouldn't.

Make constructor / destructor call init_shallow/fini_shallow,
and make those idempotent.  So, these three can be constructed
on stack now and no init/fini call is needed.  As such,
hb_auto_t<> is not needed anymore.  I'll remove that separately.

Older C++ doesn't allow struct-with-constructor in union.

Newer compilers / language allows structs with constructor in union.
So, this was not actually testing anything.  Indeed, the recent
change in DISALLOW_COPY *is* making some of our types non-POD.
That broke some bots.

Just remove this since it wasn't doing much, and I'd rather have
DISALLOW_COPY.

Finally!  Catches hard-to-find errors like this:

-    const SortedArrayOf<SVGDocumentIndexEntry> docs = this+svgDocEntries;
+    const SortedArrayOf<SVGDocumentIndexEntry> &docs = this+svgDocEntries;

We implement this for our array types.  This, in turn, trickles down
into all types that embed the arrays.  So, as long as we define all
open-ended structs in terms of Array types (all can be done using
UnsizedArrayOf), this achieves the goal of making uncopyable all
structs that are variable-sized.  Yay!

Fixes https://github.com/harfbuzz/harfbuzz/issues/1299

Removes anomaly I was seeing in cpal table trying to use implicit Null(NameID).

Fixes https://github.com/harfbuzz/harfbuzz/issues/1247

Enabled if script tag 'Qaag' is passed to HarfBuzz.  Disables mark
advance-zeroing and fallback mark-positioning.

Fixes https://github.com/harfbuzz/harfbuzz/issues/1162

We never tested compiling without it.  Just kill it.  We always build
our own shaper.

Instead of passing a CFLAG/CXXFLAG to define HB_EXTERN, define it
directly in src/hb.hh as __declspec(dllexport) extern when we are
building HarfBuzz as DLLs on Visual Studio.  Define HB_INTERNAL
as nothing without defining HB_NO_VISIBILITY when building HarfBuzz as
DLLs to avoid linker errors on Visual Studio builds.

Also "install" harfbuzz-subset.dll into $(PREFIX)\bin as the
hb-subset utility will depend on that DLL at runtime, when HarfBuzz is
built as DLLs.  Since it consists of private APIs that are subject to
change, we do not install its headers nor .lib file.

Some clang versions define static_assert as a macro apparently, so we cannot
redefine it...

This reverts commit 94bfea0c.
This reverts commit 4e626278.

So we don't accidentally break it again.

Sorry for the noise, downstream custom builders.  Please adjust.

Fixes https://github.com/harfbuzz/harfbuzz/issues/1127

Also remove "    " null data for Tag.  Just use zeroes.

To help TSan and be more "correct".

Should fix bots again.

Should fix Windows build again.

It uses constexpr...