[libc-commits] [libc] [libc] Add limits.h header. (PR #78887)

[Nick Desaulniers via libc-commits]

================
@@ -0,0 +1,247 @@
+//===-- Definition of macros from limits.h --------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef __LLVM_LIBC_MACROS_LIMITS_MACROS_H
+#define __LLVM_LIBC_MACROS_LIMITS_MACROS_H
+
+#if __has_include_next(<limits.h>)
+
+// Suppress `#include_next is a language extension` warnings.
+#ifdef __clang__
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wgnu-include-next"
+#elif defined(__GNUC__) // gcc
+#if !defined _GCC_LIMITS_H_
----------------
nickdesaulniers wrote:

These two can be combined.

```c
#elif defined(__GNUC__) && !defined(_GCC_LIMITS_H_)
```

Make sure to be consistent in:
1. your use of `ifdef` for simple macros, vs `if defined` when there's multiple things to check.
2. your use of `()` around the token being checked.

https://github.com/llvm/llvm-project/pull/78887