message: Hide symbols on mac with -fvisibility=hidden
  Ref
diff: "cflags": [],
  "cflags!": [ "-fno-tree-vrp"]
  }],
  + ["OS == 'mac'", {
  + "cflags+": ["-fvisibility=hidden"],
  + "xcode_settings": {
  + "GCC_SYMBOLS_PRIVATE_EXTERN": "YES" # -fvisibility=hidden
  + }
  + }],
  ["OS == 'android'", {
  "cflags": [ "-fPIC" ],
  "ldflags": [ "-fPIC" ],
  