4.9.0-rc18: remove unused JSC::MasqueradesAsUndefined enum

Binary packages for Debian 10 (i386 and armhf), Arch (pentium4) and FreeBSD (i386) provided, highlights:

• D-Bus atleast v1.5.12 is required
• MySQL/MariaDB atleast v4.1.13 is required
• completed headers compatibility
• compiler features introduced in C++11 are assumed to be supported by the compiler
• strcasecmp(), strncasecmp(), realpath() and unsetenv() C functions are required now
• getpwnam_r(), getpwuid_r(), aswell as other C functions are checked for during build rather than hardcoding the assumption they are present for certain hosts
• Large File Support (LFS) is enabled only if the host supports all required functions, affects other projects too
• improved X11 cursor names aliases support by adding more aliases
• reimplemented QLocale::textDirection() via ICU
• implemented QFileSystemEngine::copyFile() for non-Linux platforms
• introduced QT_BUFFSIZE definition, defined in qplatformdefs header
• introduced qChecksum32() function for computing CRC-32 checksums
• introduced QLocale::MeasurementSystem::UKSystem enum and measurement system is obtained via ICU
• introduced backtrace on crash support via Unwind
• introduced qFmod() math function
• qExp() math function can handle float type
• _USE_MATH_DEFINES is defined in qmath header which means constants such as M_PI will be defined when including it
• Q_FUNC_INFO uses __PRETTY_FUNCTION__ when compiler is GCC/Clang, __func__ if other
• QFile::exists() returns true only for paths which are either file or symbolic link resolving to file
• plugged QTextBoundaryFinder and QAbstractItemModel memory leaks
• fixed various FreeBSD compatibility issues related to C functions, LFS and general file handling
• fixed QFileSystemWatcher regression since 28b8a59 affecting only the fallback polling engine
• fixed QImage regression since e939427 affecting only comparison
• fixed QSettings regression since d236165 affecting pending changes writing
• fixed QAction regression since d504e5d affecting actions visibility
• fixed QDBusConnection regression since badb333 affecting asynchronous message delivery
• fixed compatibility Q_FOREACH() affecting other projects build with GCC v9.2.0 and possibly newer versions
• fixed possbile crashes due to invalid free() in QMap, condition for the crash was guaranteed if build with GCC and LTO
• fixed possible crash and file name collisions in QTemporaryFile, default template length is 10
• fixed possible miss-compilation of QFileSystemEngine::createDirectory() and QFileSystemEngine::removeDirectory()
• fixed regression since 82f1d03 affecting QTextStream and users of QTextCodecwith QTextCodec::IgnoreHeader in state flags
• fixed upstream QTBUG-11223
• dropped deprecated D-Bus annotation name support
• dropped support for a.out format
• dropped Motif Drag-And-Drop (DND) support
• dropped LPR support
• dropped DEC Ultrix and Reliant UNIX (SINIX) support
• lots of cleanups, optimizations and fixes