Re: master 37889523278: Add new `swap` macro and use it

[Gregory Heytings]

> Did Stefan's change break some build?  If so, which build became broken 
> and why?

FYI, Stefan's change did not break any build.  "typeof" is supported by 
all compilers with which Emacs can be built, either with the keyword 
"typeof" or with the keyword "__typeof__".  The only notable compiler that 
does not support "typeof" is MSVC, with which Emacs cannot be built.

"typeof" will, moreover, officially become part of Standard C in a few 
weeks.  In doing so, the standard committee did not add something new to 
the language, but instead codified existing practice.  You can see this in 
the rationale for that change [1], which says:

"Every implementation in existence since C89 has an implementation of 
typeof. Some compilers (GCC, Clang, EDG, tcc, and many, many more) expose 
this with the implementation extension typeof. [...] This feature is the 
most "existing practice"-iest feature to be proposed to the C Standard, 
possibly in the entire history of the C standard. The feature was also 
mentioned in an "extension round up" paper that went over the state of C 
Extensions in 2007. typeof was also considered an important extension 
during the discussion of that paper, but nobody brought forth the paper 
previously to make it a reality."

[1] https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2619.htm