How to reproduce

Put MAKEFLAGS=L into your environment. Yes, that's actually for nmake, let's just pretend it makes sense.

Then, build.

Outcome

There will be some output from mingw32-make:

mingw32-make: Symbolic links not supported: disabling -L.
E:/QtCommercial/Tools/mingw730_64/bin/mingw32-make -f Makefile.Debug
mingw32-make[1]: Entering directory 'E:/bugreports/QTBUG/build-qtbug72237-Desktop_Qt_5_12_2_MinGW_64_bit-Debug'
mingw32-make[1]: Nothing to be done for 'first'.
mingw32-make[1]: Leaving directory 'E:/bugreports/QTBUG/build-qtbug72237-Desktop_Qt_5_12_2_MinGW_64_bit-Debug'

The build succeeds with that additional warning from MinGW.

mingw32-make: Symbolic links not supported: disabling -L.

This message is categorized as error in the issues pane.

Consequently, QtC pops up a question message box "There were build errors, you really wanna run?"

Expectation

If possible, unimportant warnings like this should not be handled as warnings, not errors.