make configure -list-features print the section field

prefix it to the purpose field. this makes the presentation more
consistent with the graphical tool, and avoids the need to be redundant
in the description.

Change-Id: Iea58885637e0518aa1ec2f69ff05090b7e1e77a9
Reviewed-by: Stephan Binner <stephan.binner@basyskom.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

mkspecs/features/qt_configure.prf

@@ -1919,8 +1919,10 @@ qtConfCheckErrors()
         for (k, $${currentConfig}.features._KEYS_) {
             pp = $$eval($${currentConfig}.features.$${k}.purpose)
             !isEmpty(pp) {
+                pfx = $$eval($${currentConfig}.features.$${k}.section)
+                !isEmpty(pfx): pfx = "$$pfx: "
                 all_ft += $$qtConfPadCols($$k, ".......................", \
-                                          $$section(pp, $$escape_expand(\\n), 0, 0))
+                                          $$pfx$$section(pp, $$escape_expand(\\n), 0, 0))
             }
         }
     }