Make users of `download-ci-llvm` download a new version

src/bootstrap/bootstrap.py

@@ -435,7 +435,9 @@ class RustBuild(object):
             llvm_sha = subprocess.check_output([
                 "git", "log", "--author=bors", "--format=%H", "-n1",
                 "-m", "--first-parent",
-                "--", "src/llvm-project"
+                "--",
+                "src/llvm-project",
+                "src/bootstrap/download-ci-llvm-stamp",
             ]).decode(sys.getdefaultencoding()).strip()
             llvm_assertions = self.get_toml('assertions', 'llvm') == 'true'
             if self.program_out_of_date(self.llvm_stamp(), llvm_sha + str(llvm_assertions)):

src/bootstrap/download-ci-llvm-stamp

@@ -0,0 +1,4 @@
+Change this file to make users of the `download-ci-llvm` configuration download
+a new version of LLVM from CI, even if the LLVM submodule hasn’t changed.
+
+Last change is for: https://github.com/rust-lang/rust/pull/78131