Replace run_compiler with RunCompiler builder pattern.

RunCompiler::new takes non-optional params, and optional
params can be set using set_*field_name* method.
finally `run` will forward all fields to `run_compiler`.

src/test/ui-fulldeps/compiler-calls.rs

@@ -26,13 +26,8 @@ fn main() {
     let mut count = 1;
     let args = vec!["compiler-calls".to_string(), "foo.rs".to_string()];
     rustc_driver::catch_fatal_errors(|| {
-        rustc_driver::run_compiler(
-            &args,
-            &mut TestCalls { count: &mut count },
-            None,
-            None,
-            None,
-        ).ok();
-    }).ok();
+        rustc_driver::RunCompiler::new(&args, &mut TestCalls { count: &mut count }).run().ok();
+    })
+    .ok();
     assert_eq!(count, 2);
 }