Building environment using system headers instead of the in-tree headers

[Xin Li]

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Hi,

Josh Paetzel recently discovered an interesting build issue with the
current FreeBSD 'buildworld', where 'make buildworld' over a FreeBSD
9.0 tree on a FreeBSD 9.1 system will fail.

As it turns out, this was caused by addition of xlocale functionality
on FreeBSD 9.1, which uses macros and expects some new functions found
in more recent FreeBSD releases.  On the other hand, we do not pass
e.g. -I${.CURDIR}/../../include so the header is preferred than system
header.

So an obvious way to get around this would be to add that to CFLAGS.
It looks like that in r81600 Peter have "sneak in" such change in libc
because the FILE structure was changed and we have to use that to get
the code compile.

Thinking about the problem, it seems to be reasonable to do it for all
Makefile's as that would bring more consistent compiling results.  Is
there any reason not to do this?  If no then I will work on changing
the build infrastructure to implement that and send the patch for review.

Comments or objections?

Cheers,
- -- 
Xin LI <delphij at delphij.net>    https://www.delphij.net/
FreeBSD - The Power to Serve!           Live free or die
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