Make linker call look great again

Fix issues with messed up linker path:

 * do not use LIBS_PRIVATE on linux at least for passing object
   and archive responses files.
 * do not use QT and QT_PRIVATE with same libs, it simply
   includes libs in LIB and LIB_PRIVATE so doubles linker libs.
 * remove bogus dependency for gui and core for webengineheaders pseudo module.
 * remove unused egl config flag

Fixes: QTBUG-75832
Task-number: QTBUG-75357
Change-Id: I1720394e636e3f89d546f372b10932dd4ad395fe
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>