Fix linking against imm32 with mingw-w64

Change-Id: Id026f83dcd0da6faf1f8ff3a5d453d2e762f1231
Reviewed-by: Jarkko Koivikko <jarkko.koivikko@code-q.fi>
(cherry picked from commit a3882d6c

)
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

src/plugin/CMakeLists.txt

@@ -42,7 +42,7 @@ qt_internal_extend_target(QVirtualKeyboardPlugin CONDITION disable-layouts
 
 qt_internal_extend_target(QVirtualKeyboardPlugin CONDITION WIN32
     LIBRARIES
-        Imm32.lib
+        imm32
 )
 
 #### Keys ignored in scope 4:.:.:plugin.pro:WIN32: