FindOpenMP: Save flags/libs in cache entries each time they are detected

Modules/FindOpenMP.cmake

@@ -425,13 +425,12 @@ foreach(LANG IN ITEMS C CXX)
     if(NOT DEFINED OpenMP_${LANG}_FLAGS OR "${OpenMP_${LANG}_FLAGS}" STREQUAL "NOTFOUND"
       OR NOT DEFINED OpenMP_${LANG}_LIB_NAMES OR "${OpenMP_${LANG}_LIB_NAMES}" STREQUAL "NOTFOUND")
       _OPENMP_GET_FLAGS("${LANG}" "${LANG}" OpenMP_${LANG}_FLAGS_WORK OpenMP_${LANG}_LIB_NAMES_WORK)
+      set(OpenMP_${LANG}_FLAGS "${OpenMP_${LANG}_FLAGS_WORK}"
+        CACHE STRING "${LANG} compiler flags for OpenMP parallelization" FORCE)
+      set(OpenMP_${LANG}_LIB_NAMES "${OpenMP_${LANG}_LIB_NAMES_WORK}"
+        CACHE STRING "${LANG} compiler libraries for OpenMP parallelization" FORCE)
+      mark_as_advanced(OpenMP_${LANG}_FLAGS OpenMP_${LANG}_LIB_NAMES)
     endif()
-
-    set(OpenMP_${LANG}_FLAGS "${OpenMP_${LANG}_FLAGS_WORK}"
-      CACHE STRING "${LANG} compiler flags for OpenMP parallelization")
-    set(OpenMP_${LANG}_LIB_NAMES "${OpenMP_${LANG}_LIB_NAMES_WORK}"
-      CACHE STRING "${LANG} compiler libraries for OpenMP parallelization")
-    mark_as_advanced(OpenMP_${LANG}_FLAGS OpenMP_${LANG}_LIB_NAMES)
   endif()
 endforeach()