Starting from C++11, several math functions, like isinf, moved into the std
namespace. Since cmath undefines those functions before redefining them inside
the namespace, and glibc 2.23 defines the C variants as macros, the C variants
in global namespace are not accessible any longer.

v2: Move the fix outside of Nouveau, as suggested by Jose Fonseca, since anyone
    might need it when GCC switches to C++14 by default with GCC 6.0.

v3:
*   Put the code directly inside c99_math.h rather than creating a new header
    file, as asked by Jose Fonseca;
*   Guard the code behind glibc version checks, as only glibc > =2.23 defines
    isinf & co. as functions, as suggested by Jose Fonseca.

Signed-off-by: Pierre Moreau <pierre.morrow@free.fr>
Signed-off-by: Jose Fonseca <jfonseca@vmware.com>

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>

Unsurprisingly doesn't build otherwise with old msvc.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>

The fpclassify stuff either needs std=c99 or _XOPEN_SOURCE=600 passed
to gcc, but when using the latter the lrint family of function will be defined
too.

MSVC 2013 declares these functions, both for C and C++ source files.

This was caught with MSVC in analyze mode.

Reviewed-by: Brian Paul <brianp@vmware.com>

I didn't actually hit the issue in practice, but just happen to notice
while looking at the code.

Reviewed-by: Brian Paul <brianp@vmware.com>

v2: Use #error in the #else clause, per Jose.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89342
Signed-off-by: Brian Paul <brianp@vmware.com>