Previously the assert macro took one argument named "e", but this led to
possible errors if the caller had commas in their input. C23 changed the
definition of assert to use `__VA_ARGS__` to ensure comma cases are
handled properly. This patch doesn't introduce the enforcement function
mentioned in the standard update, though that may be done in a followup.

Fixes #136184

This addresses an issue introduced in #98826 where static_assert was
made defined only when NDEBUG is not set which is different from all
other C libraries and breaks any code that uses static_assert and
doesn't guard it with NDEBUG.

- removed assert macro definitions in api.td
- included macro definitions in assert.h.def
- added assert.yaml

Fixes #87561

Performed en-masse via:

    $ grep -rn "#include <ll" libc/include -l | \
      xargs perl -pi -e 's/#include <ll(.*)>/#include "ll$1"/'
    $ grep -rn "#include <__" libc/include -l | \
      xargs perl -pi -e 's/#include <__(.*)>/#include "__$1"/'

Link: #83463
Link: #83210

Summary:
Made all header files consistent based of this documentation: https://llvm.org/docs/CodingStandards.html#file-headers.
And did the same for all source files top of file comments.

Reviewers: sivachandra, abrachet

Reviewed By: sivachandra, abrachet

Subscribers: MaskRay, tschuett, libc-commits

Tags: #libc-project

Differential Revision: https://reviews.llvm.org/D77533

Summary: This patch adds a temporary `__assert_fail` and `assert` definition to make it available to internal llvm libc code. `__assert_fail` writes to fd 2 directly instead of `stderr`, using SYS_write. I have not put it in its own linux directory because this is temporary and it should be using stdio's api in the future. It does not currently print out the line number (although we could do that by stringifying `__LINE__` if reviewers wish).

Reviewers: sivachandra, gchatelet, PaulkaToast

Reviewed By: sivachandra

Subscribers: mgorny, MaskRay, tschuett, libc-commits

Differential Revision: https://reviews.llvm.org/D75420