"introduce no new bootstrap warning" criteria. was: Loop iv debugging, patch

[Neil Booth]

Geoff Keating wrote:-

> Or perhaps the macro expander should track which macros are defined in
> system headers and not produce warnings for them?

I'm not a fan of this option at all.  The only warnings we can avoid
this way are CPP warnings about the macro definition, which one
would hope was valid anyway being in a system header.

When it comes to usage, it gets really hairy because the invocation of
the macro could have come from other macros or macro arguments,
recursively who is to know whether those tokens come from user code or
system headers?  And to the front ends, tokens all look the same
regardless of whence they came.

Zack showed Ulrich how to fix glibc to avoid the warning, and was
rudely brushed off.

Neil.