Fix cmake build for old versions (#8173)

Adresses all these issues ->
https://github.com/google/flatbuffers/issues/7994
https://github.com/google/flatbuffers/issues/7979
https://github.com/google/flatbuffers/issues/8049

Fix 7994, Fix 7979, Fix 8049

Co-authored-by: Derek Bailey <derekbailey@google.com>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index ab69955..c036885 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -556,7 +556,7 @@
 
   # Add a library so there is a single target that the generated samples can 
   # link too.
-  if(MSVC)
+  if(MSVC OR ${CMAKE_VERSION} VERSION_GREATER_EQUAL "3.20.0")
     add_library(flatsample INTERFACE)
   else()
     add_library(flatsample STATIC)