Auto merge of #46008 - alexcrichton:update-llvm, r=Mark-Simulacrum

rustbuild: Update LLVM and enable ThinLTO

This commit updates LLVM to fix #45511 (https://reviews.llvm.org/D39981) and
also reenables ThinLTO for libtest now that we shouldn't hit #45768. This also
opportunistically enables ThinLTO for libstd which was previously blocked
(#45661) on test failures related to debuginfo with a presumed cause of #45511.

Closes #45511

src/test/run-make/sanitizer-leak/Makefile

@@ -1,10 +1,19 @@
 -include ../tools.mk
 
+LOG := $(TMPDIR)/log.txt
+
+# FIXME(#46126) ThinLTO for libstd broke this test
+ifeq (1,0)
 all:
 ifeq ($(TARGET),x86_64-unknown-linux-gnu)
 ifdef SANITIZER_SUPPORT
 	$(RUSTC) -C opt-level=1 -g -Z sanitizer=leak -Z print-link-args leak.rs | grep -q librustc_lsan
-	$(TMPDIR)/leak 2>&1 | grep -q 'detected memory leaks'
+	$(TMPDIR)/leak 2>&1 | tee $(LOG)
+	grep -q 'detected memory leaks' $(LOG)
 endif
 endif
 
+else
+all:
+endif
+

src/test/run-pass/lto-still-runs-thread-dtors.rs

@@ -0,0 +1,41 @@
+// Copyright 2017 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.
+
+// compile-flags: -C lto
+// no-prefer-dynamic
+// ignore-emscripten no threads support
+
+use std::thread;
+
+static mut HIT: usize = 0;
+
+thread_local!(static A: Foo = Foo);
+
+struct Foo;
+
+impl Drop for Foo {
+    fn drop(&mut self) {
+        unsafe {
+            HIT += 1;
+        }
+    }
+}
+
+fn main() {
+    unsafe {
+        assert_eq!(HIT, 0);
+        thread::spawn(|| {
+            assert_eq!(HIT, 0);
+            A.with(|_| ());
+            assert_eq!(HIT, 0);
+        }).join().unwrap();
+        assert_eq!(HIT, 1);
+    }
+}