accommodating OS/x, bleeding edge gcc and warnings

[Jim Meyering]

With very recent gcc and all warnings enabled for grep's subset of
gnulib, I was seeing warnings about functions that deserve pure, const
and gnu_printf attributes.

Here are patches to avoid those:

0001-fpending-obstack-strerror-override-use-pure-const-fu.patch
Description: Binary data

0002-error-make-the-module-depend-on-vfprintf-posix.patch
Description: Binary data