Allow installing to a local sitelib

Such as a virtual environment

Contributes to CURA-8640

CMakeLists.txt

@@ -43,6 +43,11 @@ if(APPLE)
 endif()
 find_package(Python ${Python_VERSION} EXACT REQUIRED COMPONENTS Interpreter)
 message(STATUS "Linking and building ${project_name} against Python ${Python_VERSION}")
+if(NOT DEFINED Python_SITELIB_LOCAL)
+    set(Python_SITELIB_LOCAL
+            ${Python_SITELIB}
+            CACHE PATH "Local alternative site-package location to install Cura" FORCE)
+endif()
 
 # Tests
 include(CuraTests)
@@ -72,10 +77,10 @@ if(NOT APPLE AND NOT WIN32)
             DESTINATION ${CMAKE_INSTALL_BINDIR}
             PERMISSIONS OWNER_READ OWNER_WRITE OWNER_EXECUTE GROUP_READ GROUP_EXECUTE WORLD_READ WORLD_EXECUTE)
     install(DIRECTORY cura
-            DESTINATION ${Python_SITELIB}/cura
+            DESTINATION ${Python_SITELIB_LOCAL}/cura
             FILES_MATCHING PATTERN *.py)
     install(FILES ${CMAKE_BINARY_DIR}/CuraVersion.py
-            DESTINATION ${Python_SITELIB}/cura)
+            DESTINATION ${Python_SITELIB_LOCAL}/cura)
 
     install(FILES ${CMAKE_BINARY_DIR}/com.ultimaker.cura.desktop
             DESTINATION ${CMAKE_INSTALL_DATADIR}/applications)
@@ -91,8 +96,8 @@ else()
             DESTINATION ${CMAKE_INSTALL_BINDIR}
             PERMISSIONS OWNER_READ OWNER_WRITE OWNER_EXECUTE GROUP_READ GROUP_EXECUTE WORLD_READ WORLD_EXECUTE)
     install(DIRECTORY cura
-            DESTINATION ${Python_SITELIB}
+            DESTINATION ${Python_SITELIB_LOCAL}
             FILES_MATCHING PATTERN *.py)
     install(FILES ${CMAKE_BINARY_DIR}/CuraVersion.py
-            DESTINATION ${Python_SITELIB}/cura)
+            DESTINATION ${Python_SITELIB_LOCAL}/cura)
 endif()