Linker error: libqbsscriptengine.so.1.21 not found

1. Clone Creator's sources:

   git clone -b 6.0 git://code.qt.io/qt-creator/qt-creator.git creator-6
   

2. Initialize the submodules:

   cd creator-6
   git submodule update --init --recursive
   

3. In an empty directory, try building from these sources using qmake:

   qmake ~/dev/src/creator-6/qtcreator.pro && make
   

   You will run into linker errors, starting with:

   /usr/bin/ld: warning: libqbsscriptengine.so.1.21, needed by /home/qtrob/dev/g++-11.1.0/creator-6-6.2.1-qmake/lib/qtcreator/libqbscore.so, not found (try using -rpath or -rpath-link)
   /usr/bin/ld: /home/qtrob/dev/g++-11.1.0/creator-6-6.2.1-qmake/lib/qtcreator/libqbscore.so: undefined reference to `QScriptEngine::qt_metacast(char const*)'
   /usr/bin/ld: /home/qtrob/dev/g++-11.1.0/creator-6-6.2.1-qmake/lib/qtcreator/libqbscore.so: undefined reference to `QTextCodec::toUnicode(QByteArray const&) const'
   /usr/bin/ld: /home/qtrob/dev/g++-11.1.0/creator-6-6.2.1-qmake/lib/qtcreator/libqbscore.so: undefined reference to `QScriptString::QScriptString(QScriptString const&)'
   

The mentioned file is present in Creator's build directory:

[qtrob@tt creator-6-6.2.1-qmake]$ find -name libqbsscriptengine.so\*
./lib/qtcreator/libqbsscriptengine.so.1.21
./lib/qtcreator/libqbsscriptengine.so.1.21.0
./lib/qtcreator/libqbsscriptengine.so
./lib/qtcreator/libqbsscriptengine.so.1

This builds fine with Qt 5.15.2 from Manjaro's repos.