QtQuickCompiler, FileSelectors & MinGW Library Linker not compatible

There is a special case where current QtQuickCompiler breaks when building a library with provided MinGW 5.3 toolchain:

Setup:

• Create a project with more than 10 QML and/or C++ files
• Add one QML file in a file selector subdirectory (e.g. "+selector/file.qml")
• Use a QRC file for the project (default)
• Enable QtQuickCompiler with "CONFIG += qtquickcompiler"
• Build a static library with "TEMPLATE = lib" and "CONFIG += staticlib"
• Build the project with prebuilt "Desktop Qt 5.11.1 MinGW 32bit" Kit

Result:

The build fails during linking with an error like: "ar: can't open file selector_file_qml.o".

 Reason:

If providing more than 10 linker files, qmake creates a script file that's passed to ar instead of providing the object files on the command line (configured with QMAKE_LINK_OBJECT_MAX in mkspecs). This is to prevent an issue with hitting max. chars possible on command line on Windows.

MinGW ar linker now reads in a line like "./debug+selector_file_qml.o". The "+" might be interpreted as a line separator, which results in reading in an incomplete filename. This might be related to MinGW bug: https://sourceforge.net/p/mingw/bugs/1429/ . The linker finally fails because of the malformed filename.

This does not happen if you:

• Increase QMAKE_LINK_OBJECT_MAX (might hit the maximum line length though)
• Build a shared library or app (the resulting object_script file has different syntax then; INPUT() instead of ADDMOD lines)
• Do not use file selectors or do not use QtQuickCompiler with MinGW obviously

Another quickfix might be to strip out "+" chars from generated CPP files of qmlcachegen call (qmlCacheOutputName defineReplace method).

Is that a known issue at the moment? Any workarounds despite the mentioned ones? Will this be fixed with upcoming MinGW 7 toolchain?