fix mingw compile error by resolving std::min type mismatch (#346)

Co-authored-by: Weining Wu <wnwu@fortinet.com>

src/fdr/fdr_engine_description.cpp

@@ -71,7 +71,7 @@ u32 findDesiredStride(size_t num_lits, size_t min_len, size_t min_len_count) {
         } else if (num_lits < 5000) {
             // for larger but not huge sizes, go to stride 2 only if we have at
             // least minlen 3
-            desiredStride = std::min(min_len - 1, 2UL);
+	     desiredStride = std::min(min_len - 1, static_cast<std::size_t>(2UL));
         }
     }