Update LLVM to fix crash on Emscripten targets

Adds a small Rust regression test for rust-lang#66308.

r? @alexcrichton

Author: tlively

src/test/ui/issues/issue-66308.rs

@@ -0,0 +1,8 @@
+// build-pass
+// compile-flags: --crate-type lib
+
+// Regression test for LLVM crash affecting Emscripten targets
+
+pub fn foo() {
+    (0..0).rev().next();
+}