Fix exports for shared libraries

We use "shared" to define a shared library and not dll.

Change-Id: Ia97ebd0042a7ef0f33eadaa448d9a44b42331ad1
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>

src/plugins/cpptools/cpptoolsunittestfiles.pri

@@ -1,6 +1,6 @@
 # Currently there are no tests for the project explorer plugin, but we include
 # headers from it that needs to have the export/import adapted for Windows.
-contains(CONFIG, dll) {
+shared {
     DEFINES += CPPTOOLS_LIBRARY
     DEFINES += PROJECTEXPLORER_LIBRARY
 } else {