Fix run-pass tests to have 'pub fn main'

This is required by the check-fast target because each test is slurped up into a
submodule.
diff --git a/src/test/run-pass/pub-extern-privacy.rs b/src/test/run-pass/pub-extern-privacy.rs
index 360ac75..e4e260a 100644
--- a/src/test/run-pass/pub-extern-privacy.rs
+++ b/src/test/run-pass/pub-extern-privacy.rs
@@ -7,7 +7,7 @@
 }
 
 #[fixed_stack_segment] #[inline(never)]
-fn main() {
+pub fn main() {
     unsafe {
         a::free(transmute(0));
     }