Still does that if get_null() returns nullptr.  Our shaper data objects
are like that.  Shrug.

Fixes https://oss-fuzz.com/v2/testcase-detail/5754863779053568

Ouch :).

Follow up on b4c61130

Fixes https://github.com/harfbuzz/harfbuzz/issues/1374

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.

Show up with gcc -O0.

There's a few more but those are functions that need to be filled in.

Maybe this is a lost battle...

Add pointer cast operator and plus operator.

Fixes https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=11034

Was givin a dozen of:

../../src/hb-machinery.hh: In member function ‘bool AAT::ankr::sanitize(hb_sanitize_context_t*) const’:
../../src/hb-machinery.hh:307:23: warning: missed loop optimization, the loop counter may overflow [-Wunsafe-loop-optimizations]
     bool ok = --this->max_ops > 0 &&
               ~~~~~~~~~~~~~~~~~~~~~~
        this->start <= p &&
        ~~~~~~~~~~~~~~~~~~~
        p <= this->end &&
        ~~~~~~~~~~~~~~~^~
        (unsigned int) (this->end - p) >= len;
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I believe those are bogus, but this silences them and does not introduce
logic issues I believe.

For 329f2401

max_ops is signed.

Since we consume it legitimately during shaping.

Ugly, but...
Fixes https://github.com/harfbuzz/harfbuzz/issues/1227

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.

Fix a bug in CBDT sanitize, and redundant check in avar.

Technically, static const needs an out-of-class definition.  Eg:

  CXXLD    libharfbuzz-subset.la
Undefined symbols for architecture x86_64:
  "OT::FeatureVariationRecord::min_size", referenced from:
      bool OT::GSUBGPOS::subset<OT::PosLookup>(hb_subset_context_t*) constin libharfbuzz_subset_la-hb-subset.o
      bool OT::GSUBGPOS::subset<OT::SubstLookup>(hb_subset_context_t*) constin libharfbuzz_subset_la-hb-subset.o
  "OT::Record<OT::LangSys>::min_size", referenced from:
      OT::Script::subset(hb_subset_context_t*) constin libharfbuzz_subset_la-hb-subset.o
  "OT::IntType<unsigned short, 2u>::min_size", referenced from:
      OT::Script::subset(hb_subset_context_t*) constin libharfbuzz_subset_la-hb-subset.o
      OT::RecordListOf<OT::Feature>::subset(hb_subset_context_t*) const  in libharfbuzz_subset_la-hb-subset.o
ld: symbol(s) not found for architecture x86_64
collect2: ld returned 1 exit status
make[4]: *** [libharfbuzz-subset.la] Error 1
make[3]: *** [all-recursive] Error 1
make[2]: *** [all] Error 2
make[1]: *** [all-recursive] Error 1
make: *** [all] Error 2
Exited with code 2

Why does subset plan not have a hb_set_t of glyphs?

Add subset() call for GSUBGPOS struct and its dependencies.
Not hooked up anywhere.

We're going to (finally) use virtual methods for hb_serialize_context_t
customization, so don't need to carry a Serializer template variable
around...  Simplifies code.