Difficulty changing c++17 to c++11 on Vscode

Few months ago I tried compiling c++11. I followed the instructions here but then I received these following errors:

error: 
      function-like macro '__GLIBC_PREREQ' is not defined
#if __GLIBC_PREREQ(2,15) && defined(_GNU_SOURCE)
    ^
In file included from wdq.cpp:1:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/bits/stdc++.h:33:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/cuchar:53:11: fatal error: 
      'uchar.h' file not found
 #include <uchar.h>

I've constantly tried over and over again but im at the point im about to give up because im constantly wasting my time with this.

I tried re writing files but more errors kept on coming and coming so I desperately need help with this.

If someone can help me fix this issue that would be incredibly helpful to me:)

Thank you.