add cache variable for pthread-flag

src/CMakeLists.txt

@@ -46,11 +46,19 @@ add_library(fortran-support
 
 add_library(${PROJECT_NAME}::fortran-support ALIAS fortran-support)
 
-#if(CMAKE_Fortran_COMPILER_ID MATCHES "^NAG")
+if(CMAKE_Fortran_COMPILER_ID MATCHES "^NAG")
   set(THREADS_PREFER_PTHREAD_FLAG OFF)
-#else()
-#  set(THREADS_PREFER_PTHREAD_FLAG ON)
-#endif()
+  if(DEFINED HAVE_PTHREAD_H)
+      set(PTHREADS_LINK_FLAG "-lpthread" CACHE STRING "Flag used to make pthread available")
+  endif()
+else()
+  set(THREADS_PREFER_PTHREAD_FLAG ON)
+  if(DEFINED HAVE_PTHREAD_H)
+      set(PTHREADS_LINK_FLAG "-pthread" CACHE STRING "Flag used to make pthread available")
+  endif()
+endif()
+
+
 
 find_package(Threads REQUIRED)
 target_link_libraries(${PROJECT_NAME} PRIVATE Threads::Threads)