rename cmake compile flag to CIVETWEB_SSL_OPENSSL_API_1_1

This name seems more concistent with other flags

CMakeLists.txt

@@ -399,7 +399,7 @@ else()
     add_definitions(-DCRYPTO_LIB="${CIVETWEB_SSL_CRYPTO_LIB}")
   endif()
 endif()
-if(OPENSSL_API_1_1)
+if(CIVETWEB_SSL_OPENSSL_API_1_1)
   add_definitions(-DOPENSSL_API_1_1)
 endif()
 add_definitions(-DUSE_STACK_SIZE=${CIVETWEB_THREAD_STACK_SIZE})