[OpenMP][NFC] Fix warning for OpenMP standalone build (#93463)

PR #75125 introduced upward propagation of some OMPT-related CMake
variables.
For stand-alone builds this results in a warning that `SCOPE_PARENT` has
no meaning in a top-level directory.

Author: jprotze

openmp/CMakeLists.txt

@@ -137,8 +137,10 @@ if (OPENMP_ENABLE_OMPT_TOOLS)
 endif()
 
 # Propagate OMPT support to offload
-set(LIBOMP_HAVE_OMPT_SUPPORT ${LIBOMP_HAVE_OMPT_SUPPORT} PARENT_SCOPE)
-set(LIBOMP_OMP_TOOLS_INCLUDE_DIR ${LIBOMP_OMP_TOOLS_INCLUDE_DIR} PARENT_SCOPE)
+if(NOT ${OPENMP_STANDALONE_BUILD})
+  set(LIBOMP_HAVE_OMPT_SUPPORT ${LIBOMP_HAVE_OMPT_SUPPORT} PARENT_SCOPE)
+  set(LIBOMP_OMP_TOOLS_INCLUDE_DIR ${LIBOMP_OMP_TOOLS_INCLUDE_DIR} PARENT_SCOPE)
+endif()
 
 option(OPENMP_MSVC_NAME_SCHEME "Build dll with MSVC naming scheme." OFF)