Revert "xfail some tests that hang (instead of segfaulting) since eafb6789a2"

This reverts commit 5f44a1356e.

Issue #936

src/test/compile-fail/extfmt-non-literal2.rs

@@ -1,8 +1,5 @@
 // error-pattern: literal
 
-// xfail-test (issue #936)
-
-
 fn main() {
     // #fmt's first argument must be a literal.  Hopefully this
     // restriction can be eased eventually to just require a

src/test/compile-fail/extfmt-too-many-args.rs

@@ -1,7 +1,5 @@
 // error-pattern:too many arguments
 
-// xfail-test (issue #936)
-
 use std;
 
 fn main() { let s = #fmt["%s", "test", "test"]; }