Avoid magic in TSynthLocation definition

This improves performance, because in this case magic is not beneficial.

Author: owen-mc

go/ql/lib/semmle/go/internal/Locations.qll

@@ -11,12 +11,19 @@ newtype TLocation =
   TSynthLocation(string filepath, int startline, int startcolumn, int endline, int endcolumn) {
     any(DataFlow::Node n).hasLocationInfo(filepath, startline, startcolumn, endline, endcolumn) and
     // avoid overlap with existing DB locations
-    not exists(File f |
-      locations_default(_, f, startline, startcolumn, endline, endcolumn) and
-      f.getAbsolutePath() = filepath
-    )
+    not existingDBLocation(filepath, startline, startcolumn, endline, endcolumn)
   }
 
+pragma[nomagic]
+private predicate existingDBLocation(
+  string filepath, int startline, int startcolumn, int endline, int endcolumn
+) {
+  exists(File f |
+    locations_default(_, f, startline, startcolumn, endline, endcolumn) and
+    f.getAbsolutePath() = filepath
+  )
+}
+
 /**
  * A location as given by a file, a start line, a start column,
  * an end line, and an end column.