Use #pragma clang deprecated in limits.h

[AaronBallman]

limits.h currently has the following comment:

/* LONG_LONG_MIN/LONG_LONG_MAX/ULONG_LONG_MAX are a GNU extension.  It's too bad
   that we don't have something like #pragma poison that could be used to
   deprecate a macro - the code should just use LLONG_MAX and friends.
 */

This seems like a good candidate for #pragma clang deprecated to diagnose.

[ShivanshCharak]

Hey i am new in open source can u give me some idea of the issue so I can get started with it. thanks :)

[AaronBallman]

Hi @ShivanshCharak -- sorry for not seeing your comment earlier!

I think that https://github.com/llvm/llvm-project/blob/main/clang/lib/Headers/limits.h#L111 could be updated to use #pragma clang deprecated similar to how we do it in: https://github.com/llvm/llvm-project/blob/main/clang/lib/Headers/stdatomic.h#L161

I think it's fine for us to mark them as explicitly deprecated because GCC documents them as being obsolete in https://www.gnu.org/software/libc/manual/html_node/Range-of-Type.html.

If you make a patch for this (https://llvm.org/docs/Contributing.html#how-to-submit-a-patch), feel free to add me as a reviewer!