Tests/FindOpenMP: Verify linking to OpenMP libraries

Previously we only verified the `_OPENMP` preprocessor symbol.

Tests/FindOpenMP/Test/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.8)
+cmake_minimum_required(VERSION 3.12)
 project(TestFindOpenMP NONE)
 include(CTest)
 
@@ -54,7 +54,7 @@ foreach(c C CXX Fortran)
   add_executable(test_var_${c} ${OpenMPTEST_SOURCE_FILE})
   separate_arguments(_OpenMP_${c}_OPTIONS NATIVE_COMMAND "${OpenMP_${c}_FLAGS}")
   target_compile_options(test_var_${c} PRIVATE "${_OpenMP_${c}_OPTIONS}")
-  target_link_libraries(test_var_${c} PRIVATE "${OpenMP_${c}_FLAGS}")
+  target_link_libraries(test_var_${c} PRIVATE ${OpenMP_${c}_LIBRARIES})
   target_include_directories(test_var_${c} PRIVATE ${OpenMP_${c}_INCLUDE_DIRS})
   set_property(TARGET test_var_${c} PROPERTY LINKER_LANGUAGE ${c})
   add_test(NAME test_var_${c} COMMAND test_var_${c})

Tests/FindOpenMP/Test/main.c

@@ -1,7 +1,10 @@
 #include <omp.h>
 int main(void)
 {
-#ifndef _OPENMP
-  breaks_on_purpose
+#ifdef _OPENMP
+  omp_get_num_threads();
+#else
+#  error "_OPENMP not defined!"
 #endif
+  return 0;
 }