libstdc++/7805: Test 18_support/numeric_limits.cc execution fails on cygwin

[Gabriel Dos Reis]

ljrittle@gcc.gnu.org writes:

|  Since this is
|     also an ix86 machine, it doesn't surprise me.  Consider a
|     patch to use the looser check specialization for your
|     platform (as long as you can rationalize it), pre-approved.

Please, NO, don't do that.  I explained the reasons of the failure in
another message which should by now be recorded in audit trail.

-- Gaby