Attempt to fix linux build error (nlohmann-json not found)

Author: lassoan

SuperBuild/External_nlohmann_json.cmake

@@ -58,6 +58,7 @@ if(NOT DEFINED ${proj}_DIR AND NOT ${CMAKE_PROJECT_NAME}_USE_SYSTEM_${proj})
       # Install directories
       -Dnlohmann_json_INSTALL_RUNTIME_DIR:STRING=${Slicer_INSTALL_THIRDPARTY_LIB_DIR}
       -Dnlohmann_json_INSTALL_LIBRARY_DIR:STRING=${Slicer_INSTALL_THIRDPARTY_LIB_DIR}
+      -DCMAKE_INSTALL_LIBDIR:STRING=${Slicer_INSTALL_THIRDPARTY_LIB_DIR} # Skip default initialization by GNUInstallDirs CMake module
       # Options
       -DCMAKE_INSTALL_PREFIX:PATH=${EP_INSTALL_DIR}
       -DBUILD_TESTING:BOOL=OFF