waf: add support for sitl build on mac

Tools/ardupilotwaf/boards.py

@@ -148,9 +148,15 @@ class Board:
                 '-O0',
             ]
 
-        env.LINKFLAGS += [
-            '-Wl,--gc-sections',
-        ]
+        if cfg.env.DEST_OS == 'darwin':
+            env.LINKFLAGS += [
+                '-Wl,-dead_strip',
+            ]
+        else:
+            env.LINKFLAGS += [
+                '-Wl,--gc-sections',
+            ]
+
 
     def build(self, bld):
         bld.ap_version_append_str('GIT_VERSION', bld.git_head_hash(short=True))

Tools/ardupilotwaf/cxx_checks.py

@@ -126,6 +126,9 @@ def ap_common_checks(cfg):
 
 @conf
 def check_librt(cfg, env):
+    if cfg.env.DEST_OS == 'darwin':
+        return True
+
     ret = cfg.check(
         compiler='cxx',
         fragment='''