[QGIS-Developer] Compile fails on RHEL7

[Henrik K]

Building on RHEL7 with GCC 10.2.1 fails here, any hints?

[ 41%] Linking CXX shared module ../../../../output/lib/qgis/server/liblandingpage.so
/opt/rh/devtoolset-10/root/usr/libexec/gcc/x86_64-redhat-linux/10/ld: CMakeFiles/landingpage.dir/qgslandingpage.cpp.o: in function `QgsProjectLoaderFilter::QgsProjectLoaderFilter(QgsServerInterface*)':
/home/wms/src/qgis-3.16.9-210812/src/server/services/landingpage/qgslandingpage.cpp:71: undefined reference to `QgsServerFilter::QgsServerFilter(QgsServerInterface*)'
/opt/rh/devtoolset-10/root/usr/libexec/gcc/x86_64-redhat-linux/10/ld: CMakeFiles/landingpage.dir/qgslandingpage.cpp.o:(.data.rel.ro._ZTI22QgsProjectLoaderFilter[_ZTI22QgsProjectLoaderFilter]+0x10): undefined reference to `typeinfo for QgsServerFilter'
/opt/rh/devtoolset-10/root/usr/libexec/gcc/x86_64-redhat-linux/10/ld: CMakeFiles/landingpage.dir/qgslandingpage.cpp.o:(.data.rel.ro._ZTV22QgsProjectLoaderFilter[_ZTV22QgsProjectLoaderFilter]+0x30): undefined reference to `QgsServerFilter::sendResponse()'
collect2: error: ld returned 1 exit status

(https://github.com/qgis/QGIS/issues/44668)

Cheers,
Henrik