[Bug c/96907] [docs] document builtins for fputc and putc

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96907

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |msebor at gcc dot gnu.org

--- Comment #6 from Martin Sebor <msebor at gcc dot gnu.org> ---
Rather than en enumerating all the functions that are handled as built-ins (and
keeping them in sync with the code) it would be simpler to state that any
function prescribed by this or that revision of a standard may be implemented
as a built-in, and suggesting to use the __has_builtin() preprocessor function
to query support for each.

Besides adding attributes to their declarations, GCC transforms calls to some
of them into others (e.g., fputs to fputc, or fprintf to fputs or fputc) or
eliminated altogether (e.g., fputs("", f)).  It might be helpful to mention
that in the manual and point users who want to avoid such transformations to
-fno-builtin-<name>.