rustc: Change the default interior vector length to 4 per science

Author: pcwalton

src/comp/back/abi.rs

@@ -104,7 +104,7 @@ const int closure_elt_bindings = 2;
 
 const int closure_elt_ty_params = 3;
 
-const uint ivec_default_length = 8u;
+const uint ivec_default_length = 4u;
 
 const uint ivec_elt_len = 0u;