User can define hb_malloc_impl, etc, to name of custom allocator functions
that have the same signature as malloc.

Not functional change (expected!).

Needed for upcoming merge-clusters fix.

Unused right now.

And add check to FLAG()

https://bugzilla.mozilla.org/show_bug.cgi?id=1167119

This reverts commit 89cbd4d9.

See discussion:
https://bugzilla.gnome.org/show_bug.cgi?id=747772

Not sure we have any right now; motivated by this:
https://bugzilla.gnome.org/show_bug.cgi?id=747772

Based on patch from Björn Breitmeyer

This code is C++ only. There isn't a single C++ compiler that fails to
understand the "inline" keyword, since it's required by C++98. Any
compiler older than C++98 is likely to choke on the template usage
further down, so this isn't necessary.

Moreover, the C++ standard says you cannot define macros.
[lib.macro.names] says "Nor shall such a translation unit define macros
for names lexically identical to keywords." -- technically, it's a
promise that the Standard Library headers won't do it, the wording means
that the entire translation unit won't do it, which implies no source
can do it.

MSVC complains about it:
fatal error C1189: #error : The C++ Standard Library forbids macroizing
keywords. Enable warning C4005 to find the forbidden macro.

Author: Thiago Macieira <thiago.macieira@intel.com>

Just to keep Windows specific workarounds in a single place.

There is a _HBMemoryBarrier() wrapper function that emulates
MemoryBarrier() behavior when it is not defined.

There is no environment (like WinCE) and the basic version
of InitializeCriticalSection is unsupported.

https://codereview.qt-project.org/#/c/92496/

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

Fixes https://github.com/behdad/harfbuzz/pull/51

Report has it that it builds (and works) now:

  https://codereview.qt-project.org/#/c/92087/

As exercised by hb-coretext .notdef code.

Based on errors seen here:
http://testresults.qt-project.org/ci/QtBase_dev_Integration/build_03837/wince70embedded-armv4i-msvc2008_Windows_7/log.txt.gz

Fully untested.

Apparently they are not (advertised as?) safe on BSD systems.
We ignore the case of static libraries.

Whitelisted on glibc, Android, and MSVC / mingw.

https://bugs.freedesktop.org/show_bug.cgi?id=82246

Some systems insist on -Wmissing-field-initializers.  We have too many,
by design.  Fix a few easy ones.

https://github.com/behdad/harfbuzz/commit/db308280488c2ee11ba865a9922eb6a0c1abeef3#commitcomment-7077778