Build compiler-rt/builtins with MSVC

src/test/run-make/compiler-rt-works-on-mingw/Makefile

@@ -0,0 +1,17 @@
+-include ../tools.mk
+
+ifneq (,$(findstring MINGW,$(UNAME)))
+ifndef IS_MSVC
+all:
+	g++ foo.cpp -c -o $(TMPDIR)/foo.o
+	ar crus $(TMPDIR)/libfoo.a $(TMPDIR)/foo.o
+	$(RUSTC) foo.rs -lfoo -lstdc++
+	$(call RUN,foo)
+else
+all:
+
+endif
+else
+all:
+
+endif

src/test/run-make/compiler-rt-works-on-mingw/foo.cpp

@@ -0,0 +1,5 @@
+// ignore-license
+extern "C" void foo() {
+    int *a = new int(3);
+    delete a;
+}

src/test/run-make/compiler-rt-works-on-mingw/foo.rs

@@ -0,0 +1,16 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+extern { fn foo(); }
+
+pub fn main() {
+    unsafe { foo(); }
+    assert_eq!(7f32.powi(3), 343f32);
+}