rewrite msvc-opt-minsize to ui test

tests/run-make/msvc-opt-minsize/Makefile

@@ -1,6 +0,0 @@
-# ignore-cross-compile
-include ../tools.mk
-
-all:
-	$(RUSTC) foo.rs -Copt-level=z 2>&1
-	$(call RUN,foo)

tests/run-make/msvc-opt-minsize/foo.rs

@@ -1,19 +0,0 @@
-#![feature(test)]
-extern crate test;
-
-fn foo(x: i32, y: i32) -> i64 {
-    (x + y) as i64
-}
-
-#[inline(never)]
-fn bar() {
-    let _f = Box::new(0);
-    // This call used to trigger an LLVM bug in opt-level z where the base
-    // pointer gets corrupted, see issue #45034
-    let y: fn(i32, i32) -> i64 = test::black_box(foo);
-    test::black_box(y(1, 2));
-}
-
-fn main() {
-    bar();
-}

tests/ui/windows/msvc-opt-minsize.rs

@@ -0,0 +1,31 @@
+// A previously outdated version of LLVM caused compilation failures on Windows
+// specifically with optimization level `z`. After the update to a more recent LLVM
+// version, this test checks that compilation and execution both succeed.
+// See https://github.com/rust-lang/rust/issues/45034
+
+//@ ignore-cross-compile
+// Reason: the compiled binary is executed
+//@ only-windows
+// Reason: the observed bug only occurs on Windows
+//@ run-pass
+//@ compile-flags: -C opt-level=z
+
+#![feature(test)]
+extern crate test;
+
+fn foo(x: i32, y: i32) -> i64 {
+    (x + y) as i64
+}
+
+#[inline(never)]
+fn bar() {
+    let _f = Box::new(0);
+    // This call used to trigger an LLVM bug in opt-level z where the base
+    // pointer gets corrupted, see issue #45034
+    let y: fn(i32, i32) -> i64 = test::black_box(foo);
+    test::black_box(y(1, 2));
+}
+
+fn main() {
+    bar();
+}