Fix DMD source links for DDox

Author: wilzbach

dpl-docs/views/layout.dt

@@ -165,6 +165,8 @@ html(lang='en-US')
             - if( modname )
               - if( modname.startsWith("core.") )
                 - project = "druntime", path_prefix = "src/";
+              - else if( modname.startsWith("dmd.") || modname.startsWith("ddmd.") )
+                - project = "dmd", path_prefix = "src/";
               - else
                 - project = "phobos", path_prefix = "";
               - if (info.docGroups.length >= 1 && !noExactSourceCodeLinks)