[v3 PATCH] Fix Tru64 bootstrap faiure: EOVERFLOW in system_error

[Roger Sayle]

This patch should restore bootstrap on alphaev67-dec-osf5.1, by adding
a configure test for EOVERFLOW being defined in <errno.h>.  The
changes are almost identical to my earlier fixes for darwin (EBADMSG)
and cygwin (ECANCELED) and as previously approved by Ben Kosnik.
http://gcc.gnu.org/ml/libstdc++/2007-09/msg00009.html
http://gcc.gnu.org/ml/libstdc++/2007-09/msg00025.html

The following patch has been tested on powerpc-apple-darwin7.9.0
with a full "make bootstrap" and top-level "make -k check" with no
new failures.  Ok for mainline?

2007-10-11  Roger Sayle  <roger@eyesopen.com>

        * acinclude.m4 (GLIBCXX_CHECK_SYSTEM_ERROR): Add EOVERFLOW for 
Tru64.
        * configure: Regenerate.
        * config/os/generic/error_constants.h: Guard.
        * testsuite/19_diagnostics/headers/system_error/
        types_std_c++0x.cc: Same.

Roger
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