cmake: fixup tests build for old CMake

This patch is a follow-up to the commit
1e5887d ("FFI: Avoid dangling
cts->L."). The `target_link_options()` feature is introduced in CMake
3.13. Unfortunately, we have distros in Tarantool's CI with an older
default CMake version.

This patch workarounds this by the passing `LINK_FLAGS` directly.

Reviewed-by: Sergey Bronnikov <sergeyb@tarantool.org>
Signed-off-by: Sergey Kaplun <skaplun@tarantool.org>
(cherry picked from commit 5f8bab2)

Author: Buristan

test/tarantool-c-tests/CMakeLists.txt

@@ -56,11 +56,11 @@ foreach(test_source ${tests})
   )
   set_target_properties(${exe} PROPERTIES
     COMPILE_FLAGS "${TESTS_C_FLAGS}"
+    # Allow to call non-static functions via FFI.
+    LINK_FLAGS "-rdynamic"
     OUTPUT_NAME "${exe}${C_TEST_SUFFIX}"
     RUNTIME_OUTPUT_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}"
   )
-  # Allow to call non-static functions via FFI.
-  target_link_options(${exe} PRIVATE "-rdynamic")
   target_link_libraries(${exe} libtest ${LUAJIT_LIBRARY})
   add_dependencies(tarantool-c-tests-build ${exe})