Add pointer cast operator and plus operator.

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/1129

Found and fixed a couple bugs.

Found a couple multithreading issues.  Marked them with "XXX-MT-bug".

Clang is being really peculiar.  Fix with:

-  inline hb_blob_t *sanitize (hb_blob_t *blob) { return c->sanitize<Type> (blob); }
+  inline hb_blob_t *sanitize (hb_blob_t *blob) { return c[0].template/*clang idiosyncrasy*/sanitize_blob<Type> (blob); }

Makes for cleaner code.

Following to 63f57f4d

Part of https://github.com/harfbuzz/harfbuzz/issues/1017

Fixes https://github.com/harfbuzz/harfbuzz/issues/934

Program: Z:\Users\ebrahim\Desktop\harfbuzz\winbuild\util\.libs\hb-shape.exe
File: ../../src/hb-open-type-private.hh, Line 769

Expression: 0 == (Length & 3)

abnormal program termination

Fixes #791.

Untested, but compiles.

Fixes https://github.com/behdad/harfbuzz/issues/615

We'll see which bots I broke.

Part of fixing https://github.com/behdad/harfbuzz/pull/605

https://travis-ci.org/behdad/harfbuzz/jobs/295039536#L3468
https://ci.appveyor.com/project/behdad/harfbuzz/build/1.0.697/job/dr1ujlntxafeqbej#L142

Shape-plan caching is not implemented.

This one:

  map->mask = (1 << (next_bit + bits_needed)) - (1 << next_bit);

before the fix, the shift was done as an int, causing overflow
if it ever got to 1 << 31.  Sprinkle 'u's around.

Fixes https://bugs.chromium.org/p/chromium/issues/detail?id=634805

This happens with at least one test font I have.

On Windows 10 we are seeing that other error message...

Test sequence: U+0995,U+-9CD,U+09B0
With Nirmala shipped on Windows 10, this failed to form the below form.
Works now.

Reported by Sairus.

Ouch!

By default shape at upem (or ppem), and scale results.
Similar to work done in CoreText backend, but using upem as default.

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=84491