[Interest] Where does libGL get changed to absolute and how to stop?

[John Cary]

Trying to configure qt-5.12.5 to use mesagl, so I modified
qtbase/mkspecs/linux-g++-64/qmake.conf
to have

QMAKE_LIBDIR_OPENGL     = 
/scr_ivy/cary/contrib-gcc830/mesa-17.2.8-sersh/lib 
/scr_ivy/cary/contrib-gcc830/llvm-5.0.0-sersh/lib
QMAKE_INCDIR_OPENGL     = 
/scr_ivy/cary/contrib-gcc830/mesa-17.2.8-sersh/include
QMAKE_LIBS_OPENGL      += -lLLVM

and early on, print shows

Project MESSAGE: QMAKE_LIBS_OPENGL = -lGL -lLLVM

But somewhere this gets changed to

Project MESSAGE: AFter currentConfig = config.qtbase: QMAKE_LIBS_OPENGL 
= /lib64/libGL.so

i.e., with a full path, and not to the path I specified with 
QMAKE_LIBDIR_OPENGL.

Is there a way to stop this behavior?

Where is the code that does this?

Thx....John Cary