build: Fix static build with Clang on macOS

build-support/macros-and-definitions.cmake

@@ -204,6 +204,7 @@ set(CMAKE_CXX_STANDARD_MINIMUM 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(LIB_AS_NEEDED_PRE)
 set(LIB_AS_NEEDED_POST)
+set(STATIC_LINK_FLAGS -static -static-libstdc++ -static-libgcc)
 if(${GCC} AND NOT APPLE)
   # using GCC
   set(LIB_AS_NEEDED_PRE -Wl,--no-as-needed)
@@ -216,6 +217,8 @@ endif()
 if(${CLANG} AND APPLE)
   # using Clang set(LIB_AS_NEEDED_PRE -all_load)
   set(LIB_AS_NEEDED_POST)
+  set(LIB_AS_NEEDED_PRE_STATIC -Wl,-all_load)
+  set(STATIC_LINK_FLAGS)
 endif()
 
 macro(SUBDIRLIST result curdir)

src/CMakeLists.txt

@@ -59,9 +59,7 @@ if(${NS3_STATIC})
 
   target_link_libraries(
     ${lib-ns3-static}
-    -static
-    -static-libstdc++
-    -static-libgcc
+    ${STATIC_LINK_FLAGS}
     ${LIB_AS_NEEDED_PRE_STATIC}
     ${ns3-external-static-libs}
     ${LIB_AS_NEEDED_POST_STATIC}