> 
> I'd like to unidef that, removing all the support for pre-ANSI
> environments.  About the only conceivable objection I can imagine is if
> someone is still using K&R C to build kernels, or if this file is
> somehow used in bootstrapping tools (e.g. to bootstrap GCC from a K&R C
> environment).
> 
As already found, this is because of preprocessing asm files, but as
an informational side note I can mention that these files cannot be
compiled with an K&R cpp anyway.  There are constructs like this:

#if !__GNUC_PREREQ__(2, 0)

which fails because an #if statement cannot expand function-like macros
the original Reiser cpp, which is used in pcc.  Some versions, like the
SunOS4 cpp, can handle this though.

-- Ragge