simplified cmake logic about openmp (#6195)

* simplified cmake logic about openmp

* address review

CMakeLists.txt

@@ -291,25 +291,21 @@ endif()
 option(WITH_OPENMP "Build with parallelization using OpenMP" TRUE)
 option(USE_HOMEBREW_FALLBACK "(macOS-only) also look in 'brew --prefix' for libraries (e.g. OpenMP)" TRUE)
 if(WITH_OPENMP)
-  if(APPLE)
-    find_package(OpenMP COMPONENTS C CXX)
-    if(NOT OpenMP_FOUND)
-      if(USE_HOMEBREW_FALLBACK)
-        # libomp 15.0+ from brew is keg-only, so have to search in other locations.
-        # See https://github.com/Homebrew/homebrew-core/issues/112107#issuecomment-1278042927.
-        execute_process(COMMAND brew --prefix libomp
-                        OUTPUT_VARIABLE HOMEBREW_LIBOMP_PREFIX
-                        OUTPUT_STRIP_TRAILING_WHITESPACE)
-        set(OpenMP_C_FLAGS "-Xpreprocessor -fopenmp -I${HOMEBREW_LIBOMP_PREFIX}/include")
-        set(OpenMP_CXX_FLAGS "-Xpreprocessor -fopenmp -I${HOMEBREW_LIBOMP_PREFIX}/include")
-        set(OpenMP_C_LIB_NAMES omp)
-        set(OpenMP_CXX_LIB_NAMES omp)
-        set(OpenMP_omp_LIBRARY ${HOMEBREW_LIBOMP_PREFIX}/lib/libomp.dylib)
-      endif()
+  find_package(OpenMP COMPONENTS C CXX)
+  if(APPLE AND NOT OpenMP_FOUND)
+    if(USE_HOMEBREW_FALLBACK)
+      # libomp 15.0+ from brew is keg-only, so have to search in other locations.
+      # See https://github.com/Homebrew/homebrew-core/issues/112107#issuecomment-1278042927.
+      execute_process(COMMAND brew --prefix libomp
+                      OUTPUT_VARIABLE HOMEBREW_LIBOMP_PREFIX
+                      OUTPUT_STRIP_TRAILING_WHITESPACE)
+      set(OpenMP_C_FLAGS "-Xpreprocessor -fopenmp -I${HOMEBREW_LIBOMP_PREFIX}/include")
+      set(OpenMP_CXX_FLAGS "-Xpreprocessor -fopenmp -I${HOMEBREW_LIBOMP_PREFIX}/include")
+      set(OpenMP_C_LIB_NAMES omp)
+      set(OpenMP_CXX_LIB_NAMES omp)
+      set(OpenMP_omp_LIBRARY ${HOMEBREW_LIBOMP_PREFIX}/lib/libomp.dylib)
       find_package(OpenMP COMPONENTS C CXX)
     endif()
-  else()
-    find_package(OpenMP COMPONENTS C CXX)
   endif()
 endif()
 if(OpenMP_FOUND)