Cannot create target "check-builtins", another target already exists

[lukaszstolarczuk]

Describe the bug

Configure error on clean build dir, the latest sycl branch (568e193).

CMake Error at cmake/modules/LLVMExternalProjectUtils.cmake:471 (add_custom_target):
  add_custom_target cannot create target "check-builtins" because another
  target with the same name already exists.  The existing target is a custom
  target created in source directory
  "/home/luke/src/llvm/compiler-rt/test/builtins".  See documentation for
  policy CMP0002 for more details.
Call Stack (most recent call first):
  runtimes/CMakeLists.txt:271 (llvm_ExternalProject_Add)
  runtimes/CMakeLists.txt:594 (runtime_default_target)

To reproduce

run:

python3 buildbot/configure.py -t RelWithDebInfo -o build_temp --cmake-gen Ninja --cmake-opt=-DLLVM_ENABLE_RUNTIMES=openmp

Environment

Ubuntu 24.04

Additional context

No response