Build fix for -no-feature-regularexpression

Change-Id: I69942195d5208985d75333a13ed0ac5ae8f595d2
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

src/plugins/imageformats/imageformats.pro

 TEMPLATE = subdirs
 SUBDIRS = \
 #    dds \
-    icns \
     tga \
     tiff \
     wbmp \
     webp
 
+qtConfig(regularexpression): \
+    SUBDIRS += icns
+
 config_libmng: SUBDIRS += mng
 config_jasper {
     SUBDIRS += jp2