[Openmp-dev] Missed cmake change

[C Bergström]

Someone missed this in the rename. It's breaking cross build so please
push asap. (We have a work-around, but it's not clean)
----------
--- a/runtime/cmake/HelperFunctions.cmake
+++ b/runtime/cmake/HelperFunctions.cmake
@@ -63,7 +63,7 @@ function(set_legal_arch return_arch_string)
         set(${return_arch_string} "Intel(R) 64" PARENT_SCOPE)
     elseif(${MIC})
         set(${return_arch_string} "Intel(R) Many Integrated Core
Architecture" PARENT_SCOPE)
-    elseif(${arch} STREQUAL "l1")
+    elseif(${LIBOMP_ARCH} STREQUAL "l1")
         set(${return_arch_string} "L1OM" PARENT_SCOPE)
     elseif(${ARM})
         set(${return_arch_string} "ARM" PARENT_SCOPE)