diff -ruN simgear-2020.1.2/CMakeLists.txt simgear-my/CMakeLists.txt
--- simgear-2020.1.2/CMakeLists.txt	2020-05-24 17:13:35.000000000 +0200
+++ simgear-my/CMakeLists.txt	2020-10-17 15:48:58.375116913 +0200
@@ -442,8 +442,6 @@
     set(WARNING_FLAGS_CXX "-Wall -fPIC -Wno-overloaded-virtual -Wno-redeclared-class-member")
     set(WARNING_FLAGS_C   "-Wall -fPIC")
     set(CMAKE_XCODE_ATTRIBUTE_CLANG_CXX_LIBRARY "libc++")
-    # fix Boost compilation :(
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -stdlib=libc++")
 
     # override CMake default RelWithDebInfo flags.
     set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-O3 -g -DNDEBUG")