This is necessary for RubyInstaller versions based on MSYS1 (Ruby < 2.4).

RubyInstaller comes bundled with zlib-1.2.7. Since the zlib1.dll is stored in the
same directory as ruby.exe, it is preferred in the Windows DLL load order.
The zlib1.dll that is bundled with fxruby is not loaded at runtime.

If we build fxruby with a newer zlib version, libpng will make use of the new
function inflateValidate() introduced in zlib-1.2.8, which results in a DLL
load error at runtime. We avoid this by sticking at zlib-1.2.7.

Disable rbx-3 for now, because it's too slow.

Output Xorg logs only in case of failure

Ubuntu doesn't provide the symlink /usr/lib/libfxscintilla.so
but only /usr/lib/libfxscintilla.so.19 .
Therefore we link against libfxscintilla.so.19 if -lfxscintilla
can not be resolved.

"gem inst glu" fails because of missing opengl header files.

It can easily replaced by rb_ary_entry().

Also make use of StringValueCStr() where it is suitable.

Update to rake-compiler-dock-0.5.1, which adds Ruby-2.3 support for Windows annd makes --disable-rubygems unnecessary