Canonicalize inputs when filtering default system paths

Contrary to expectations, various <foo>-config tools sometimes spit out
denormalized paths, which breaks the text-based filtering, as it relies
on exact matches with normalized paths.

Change-Id: I0613ed24953a3bde19939d28d09572c88b43a361
Task-number: QTBUG-39216
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>

configure

@@ -364,6 +364,7 @@ filterDefaultPaths()
 {
     local path
     path=`cat`
+    path=`"$relpath/config.tests/unix/makeabs" "$path"`
     echo "$1" | grep "^$path\$" > /dev/null || echo "$path"
 }