Support general warnings and errors in lint pass via flags and attrs. Close #1543.

src/test/compile-fail/unused-imports-warn.rs

@@ -1,5 +1,5 @@
 // error-pattern:unused import
-// compile-flags:--warn-unused-imports
+// compile-flags:-W unused-imports
 import cal = bar::c::cc;
 
 mod foo {

src/test/compile-fail/warn-ctypes-err-attr.rs

@@ -0,0 +1,10 @@
+// error-pattern:found rust type
+#[warn(err_ctypes)];
+
+#[nolink]
+native mod libc {
+    fn malloc(size: int) -> *u8;
+}
+
+fn main() {
+}

src/test/compile-fail/warn-ctypes.rs

@@ -0,0 +1,9 @@
+// compile-flags:-W err-ctypes
+// error-pattern:found rust type
+#[nolink]
+native mod libc {
+    fn malloc(size: int) -> *u8;
+}
+
+fn main() {
+}