static openmp with ndk r21+

src/CMakeLists.txt

@@ -409,7 +409,11 @@ if(NCNN_OPENMP AND (OpenMP_CXX_FOUND OR OPENMP_FOUND))
     if(NCNN_CMAKE_VERBOSE)
         message("Building with OpenMP")
     endif()
-    if(OpenMP_CXX_FOUND)
+
+    if(DEFINED ANDROID_NDK_MAJOR AND ${ANDROID_NDK_MAJOR} GREATER 20)
+        target_compile_options(ncnn PRIVATE -fopenmp)
+        target_link_libraries(ncnn PUBLIC -fopenmp -static-openmp)
+    elseif(OpenMP_CXX_FOUND)
         target_link_libraries(ncnn PUBLIC OpenMP::OpenMP_CXX)
     else()
         target_link_libraries(ncnn PRIVATE "${OpenMP_CXX_FLAGS}")