小编use*_*121的帖子

我将我的系统更新到 macOS Catalina，然后从 homebrew 安装了 gcc-9，然后我得到了缺少标题的错误，就像每个人在更新到 Mojave 后所做的那样。但是在 Catalina 上事情macOS_SDK_headers_for_macOS_10.14.pkg就不一样了，不存在的。我试图安装我朋友从他的 Mojave Mac 发送给我的旧版本，但由于系统太新而失败。然后我试图brew upgrade，brew doctor，brew cleanup，并通过App Store和重新安装Xcode11和命令行工具xcode-select --install。没有任何效果，我的叮当声也坏了！这是我用 gcc-9 编译 hello world 程序时的错误日志：

In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/wait.h:110,
                 from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/stdlib.h:66,
                 from /usr/local/Cellar/gcc/9.2.0/include/c++/9.2.0/cstdlib:75,
                 from hello.cpp:1:
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/resource.h:443:34: error: expected initializer before '__OSX_AVAILABLE_STARTING'
  443 | int     getiopolicy_np(int, int) __OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0);
      |                                  ^~~~~~~~~~~~~~~~~~~~~~~~
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/resource.h:449:39: error: expected initializer before '__OSX_AVAILABLE_STARTING'
  449 | int     setiopolicy_np(int, int, int) __OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0);
      |                                       ^~~~~~~~~~~~~~~~~~~~~~~~
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/stdlib.h:128, …