Fix additional variadic typos

src/libsyntax/feature_gate.rs

@@ -2070,7 +2070,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                 }
                 if sig.decl.c_variadic {
                     gate_feature_post!(&self, c_variadic, ti.span,
-                                       "C-varaidic functions are unstable");
+                                       "C-variadic functions are unstable");
                 }
                 if sig.header.constness.node == ast::Constness::Const {
                     gate_feature_post!(&self, const_fn, ti.span, "const fn is unstable");

src/test/ui/feature-gate/feature-gate-c_variadic.rs

@@ -1,4 +1,4 @@
 #![crate_type="lib"]
 
 pub unsafe extern "C" fn test(_: i32, ap: ...) { }
-//~^ C-varaidic functions are unstable
+//~^ C-variadic functions are unstable

src/test/ui/feature-gate/feature-gate-c_variadic.stderr

@@ -1,4 +1,4 @@
-error[E0658]: C-varaidic functions are unstable
+error[E0658]: C-variadic functions are unstable
   --> $DIR/feature-gate-c_variadic.rs:3:1
    |
 LL | pub unsafe extern "C" fn test(_: i32, ap: ...) { }