diff --git a/buildbot/osuosl/master/config/builders.py b/buildbot/osuosl/master/config/builders.py
--- a/buildbot/osuosl/master/config/builders.py
+++ b/buildbot/osuosl/master/config/builders.py
@@ -235,11 +235,18 @@
     'builddir': "clang-arm64-windows-msvc",
     'factory' : ClangBuilder.getClangCMakeBuildFactory(
                     vs="manual",
+                    checkout_flang=True,
                     test=False, # Disable testing until MCJIT failures are fixed
                     extra_cmake_args=[
                         "-DLLVM_DEFAULT_TARGET_TRIPLE=aarch64-windows-msvc",
                         "-DLLVM_HOST_TRIPLE=aarch64-windows-msvc",
                         "-DLLVM_TARGET_ARCH=AArch64",
+                        # The BUILTINS environment variable is expected to already exist
+                        # on the worker when it is launched.
+                        "-DCMAKE_EXE_LINKER_FLAGS=%BUILTINS%",
+                        "-DCMAKE_SHARED_LINKER_FLAGS=%BUILTINS%",
+                        "-DCMAKE_STATIC_LINKER_FLAGS=%BUILTINS%",
+                        "-DCMAKE_MODULE_LINKER_FLAGS=%BUILTINS%",
                         # FIXME: compiler-rt\lib\sanitizer_common\sanitizer_unwind_win.cpp assumes WIN64 is x86_64,
                         #        so, before that's fixed, disable everything that triggers its build.
                         "-DCOMPILER_RT_BUILD_SANITIZERS=OFF",