up to 5.15.5 (multitude of security fixes)

up to 5.15.5 (multitude of security fixes)

note: this is an unofficial release -- after 5.15.2 Qt no longer makes
open source 5.15 releases but code is still available in Git. this
upgrade consists of git extract of tag v5.15.5-lts from

https://code.qt.io/cgit/qt/qtwebengine.git/

along with rev d2679df (87-based branch) from:

https://code.qt.io/cgit/qt/qtwebengine-chromium.git/

additional fixes thanks to fedora:
- remaing 'TRUE' replaced (no longer defined by icu)
- syncqt.pl invocation to fix build errors related to missing header
  <QtWebEngineCore/qtwebenginecoreglobal.h>
- font rendering issue with glibc 2.33
- gold preference -- bfd got insane when it comes to opened file
  descriptors (4096 is not enough to build qtwebengine and qtwenengine
  itself enforces no more than 4096 opened descriptors limiting it even
  if user's limit is higher)