qmake generates deprected C++17 name (gnu++1z)

When specifying CONFIG += c++17 inside the Qt project file, the generated Makefile after running qmake generates -std=gnu++1z in CXXFLAGS, which according to the gcc documentation is deprecated:

gnu++17
gnu++1z
    GNU dialect of -std=c++17. The name gnu++1z is deprecated.

This makes the build fail on some systems, like the Windows cross-compiler on Fedora 31. Manually changing it to gnu++17 works as a workaround.

error: unrecognized command line option '-std=gnu++1Z'; did you mean '-std=gnu++11'?

EDIT:
After some debugging, I noticed the error is caused by qmake generating -std=gnu++1Z rather than -std=gnu++1z.