Auto merge of #49200 - oli-obk:extern_static_metadata, r=michaelwoerister

Encode/decode extern statics in metadata and incremental cache

fixes #49153

cc @abonander

r? @michaelwoerister incremental ICE

src/test/incremental/extern_static/issue-49153.rs

@@ -0,0 +1,21 @@
+// Copyright 2018 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.
+
+// https://github.com/rust-lang/rust/issues/49153
+
+// revisions:rpass1 rpass2
+
+extern "C" {
+    pub static __ImageBase: u8;
+}
+
+pub static FOO: &'static u8 = unsafe { &__ImageBase };
+
+fn main() {}