Hi all,

This macro, encountered in most headers, seems to work around some
compilers not supporting C99.  A quick internet search shows that no
other software except Emacs uses this (any more, I assume some did in
the past).

Is it still useful? If not, it unnecessarily complicates the header
structure and should be removed.

I attach an example patch for only buffer.h that compiles and works
well.

Also, what's the stance on C11? I don't know a lot of C outside of what
C++ includes, but I'm considering to learn more of it just for Emacs.
Is C11 encouraged / allowed / discouraged / disallowed?

I assume that C99 is at least allowed since #17487. Is it encouraged?
In that case, surely INLINE_HEADER_BEGIN should be removed.

Oleh