rustc: uniquely mangle expr_fn names

two closures in the same function body can end up having
the same mangled name. This small patch uses gensym to
uniquely name each closure body so there won't be conflicts.

Author: erickt

src/rustc/middle/trans/closure.rs

@@ -363,7 +363,7 @@ fn trans_expr_fn(bcx: block,
     let llfnty = type_of_fn_from_ty(ccx, fty);
     let sub_path = vec::append_one(bcx.fcx.path,
                                    path_name(special_idents::anon));
-    let s = mangle_internal_name_by_path(ccx, sub_path);
+    let s = mangle_internal_name_by_path_and_seq(ccx, sub_path, ~"expr_fn");
     let llfn = decl_internal_cdecl_fn(ccx.llmod, s, llfnty);
 
     let trans_closure_env = fn@(ck: ty::closure_kind) -> Result {