Stop erasing mkspecs/modules at every reconfigure.

Developers who are building & rebuilding Qt often end up needing to
recompile all other modules because of this removal even though the
libs are still compatible.

Change-Id: I4ec0e8ab222675dcd2a3f3a2b5e931c1c7f31f69
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>

configure

@@ -2097,6 +2097,10 @@ if [ "$OPT_SHADOW" = "yes" ]; then
         fi
     done
 
+    # save a pre-existing mkspecs/modules dir
+    test -d "$outpath/mkspecs/modules" && \
+        mv "$outpath/mkspecs/modules" "$outpath/mkspecs-modules"
+
     # symlink the mkspecs directory
     mkdir -p "$outpath/mkspecs"
     rm -rf "$outpath"/mkspecs/*
@@ -2116,7 +2120,12 @@ if [ "$OPT_SHADOW" = "yes" ]; then
     ShadowMkspecs features
 
     # The modules dir is special, too.
-    ShadowMkspecs modules
+    if test -d "$outpath/mkspecs-modules"; then
+        rm -rf "$outpath/mkspecs/modules"
+        mv "$outpath/mkspecs-modules" "$outpath/mkspecs/modules"
+    else
+        ShadowMkspecs modules
+    fi
 
     # symlink the doc directory
     rm -rf "$outpath/doc"