Harfbuzz: backporting fixes from upstream

81c8ef785b079980ad5b46be4fe7c7bf156dbf65 Fix crash!
81f2ecafa19b602f950df5a9e6e1b99c4b5ea55e Bug 30319
ff0612c2e7df1b86fc702c72e3015a6a5ae39b4c and
2dbd0fd11799c18bb6c66e337c3e31a1419823d4 Fix OOB access possibility
3bebe289aace6daa84b3d6983cebf5c58ddfad78 Fix problem with Indic shaper and control chars
90138e5a4d15c44f05456f90083ecacdc3196c8e Fix bad memory access in Myanmar shaper
b847f24ce855d24f6822bcd9c0006905e81b94d8 Fix Arabic cursive positioning
3ab7b37bdebf0f8773493a1fee910b151c4de30f Fix misc leaks

Change-Id: I6f3a6253782bff6abe4bf741d11c09fdd67542db
(cherry picked from qtbase/7df995a9bd3e989b4136f98424490604eb5178aa)
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Fix clang build on Mac OS X

Clang doesn't like the extra qualification in the forward declaration. Let's
move the forward declaration outside of the Qt namespace, which is better anyway
since TabletProximityRec is defined in the Apple headers/global namespace.

Task-number: QTBUG-29373
Change-Id: Iba59e6592ccbbcc09e91e1b9831a0ee588469b23
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>