build: auto openssl vsn when link sys crypto

CMakeLists.txt

@@ -35,14 +35,18 @@ else()
   set(CMAKE_BUILD_TYPE "RelWithDebInfo")
 endif()
 
-if (DEFINED ENV{QUICER_USE_OPENSSL3})
-  message(STATUS "Use openssl3")
-  set(QUIC_TLS "openssl3")
-endif()
-
 if (DEFINED ENV{QUIC_USE_SYSTEM_LIBCRYPTO})
-  message(STATUS "Link to system libcrypto")
+  find_package(OpenSSL REQUIRED)
+  if ("${OPENSSL_VERSION}" MATCHES "3.*")
+      set(QUIC_TLS openssl3)
+  else()
+      set(QUIC_TLS openssl)
+  endif()
   set(QUIC_USE_SYSTEM_LIBCRYPTO "ON")
+else()
+  if (DEFINED ENV{QUIC_TLS})
+    set(QUIC_TLS $ENV{QUIC_TLS})
+  endif()
 endif()
 
 if (DEFINED ENV{QUIC_ENABLE_LOGGING})