diff -up widelands-build20/CMakeLists.txt~ widelands-build20/CMakeLists.txt
--- widelands-build20/CMakeLists.txt~ 2019-05-02 07:23:39.000000000 +0200
+++ widelands-build20/CMakeLists.txt 2019-05-13 15:21:05.368834756 +0200
@@ -167,7 +167,7 @@ else()
message(FATAL_ERROR "Unknown CMAKE_BUILD_TYPE: ${CMAKE_BUILD_TYPE}")
endif()
-wl_add_flag(WL_GENERIC_CXX_FLAGS "-std=c++11")
+wl_add_flag(WL_GENERIC_CXX_FLAGS "-std=gnu++11")
if(OPTION_ASAN)
message(STATUS "Using AddressSanitizer http://clang.llvm.org/docs/AddressSanitizer.html")