Add core-private dependency to core_api.pro

We want to use private QtCore API in later commits.

Change-Id: If006d9bfd503cdb21b3adf164c0ebf2aa8967bac
Reviewed-by: Michal Klocek <michal.klocek@theqtcompany.com>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@theqtcompany.com>

src/core/api/core_api.pro

@@ -4,7 +4,7 @@ DESTDIR = $$OUT_PWD/$$getConfigDir()
 TEMPLATE = lib
 
 CONFIG += staticlib c++11
-QT += network
+QT += network core-private
 
 # Don't create .prl file for this intermediate library because
 # their contents get used when linking against them, breaking