[libc] [llvm] [libc] Provide an implementation of the 'stdint.h' header (PR #83353)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

For clarification, this patch implements a `stdint.h` that will be installed. This is useful because `stdint.h` is expected to be able to be usable from the C library but we previously didn't provide one. I used the `clang` implementation as it's correct to the standard and GCC compatible. I think in a separate patch we could move `#include <stdint.h>` to include this header instead. Though personally I don't think it will change much because it's `stdint.h` is defined by the standard to be freestanding. 

https://github.com/llvm/llvm-project/pull/83353