CMake: fix use of GNUInstallDirs

CMakeLists.txt

@@ -73,7 +73,8 @@ set(${PROJECT_NAME}_SOURCES
 
 add_library(${PROJECT_NAME} SHARED ${${PROJECT_NAME}_SOURCES}
                                    ${${PROJECT_NAME}_HEADERS})
-target_include_directories(${PROJECT_NAME} PUBLIC $<INSTALL_INTERFACE:include>)
+target_include_directories(
+  ${PROJECT_NAME} PUBLIC $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>)
 target_link_libraries(${PROJECT_NAME} PUBLIC Eigen3::Eigen qpOASES::qpOASES
                                              CDD::CDD)