diff --git a/appveyor.yml b/appveyor.yml
index d70ad54b1c812..2abf723de496e 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -1,4 +1,7 @@
 environment:
+  # This is required for at least an AArch64 compiler in one image, and is also
+  # going to soon be required for compiling LLVM.
+  APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017 Preview
 
   # By default schannel checks revocation of certificates unlike some other SSL
   # backends, but we've historically had problems on CI where a revocation
@@ -81,7 +84,6 @@ environment:
     DIST_REQUIRE_ALL_TOOLS: 1
     DEPLOY: 1
     CI_JOB_NAME: dist-x86_64-msvc
-    APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017 Preview
   - RUST_CONFIGURE_ARGS: >
       --build=i686-pc-windows-msvc
       --target=i586-pc-windows-msvc
diff --git a/src/llvm-project b/src/llvm-project
index 38ad31bde8ff6..4fc9fb8245abe 160000
--- a/src/llvm-project
+++ b/src/llvm-project
@@ -1 +1 @@
-Subproject commit 38ad31bde8ff681d862dc0f96930a5dd9b7a472e
+Subproject commit 4fc9fb8245abe24680192535870c4522644a4212