26_numerics/c99_classification_macros_c++.cc fails on cygwin

[Gabriel Dos Reis]

"Billinghurst, David (CRTS)" <David.Billinghurst@riotinto.com> writes:

| Test 26_numerics/c99_classification_macros_c++.cc fails on cygwin. 
| I have reduced the problem, but don't understand what's happening.

that means that cygwin has defined the C99 macro fpclassify and the
library couldn't get rid of it. 
The header <cmath> should not define any of those macros.  If that
testcase fails, then it means a bug in libstdc++-v3 on cygwin.

-- Gaby