CURRENT: Changes in lib/msun/math.h make ports to fail

Updating CURRENT from r253216 to r253252 triggers an updating of
several ports to fail, namely, for instance,

www/firefox
graphiks/webkit-gtk2
deskuitls/fbreader
graphics/gdal

The error is in all ports when compiled with CLANG 3.3 -std=c++11
-stdlib=libc++ similar, routing to math.h. I will show the error for
www/firefox:

[...]
In file included from ./../../dist/include/mozilla/MathAlgorithms.h:15:
/usr/include/c++/4.2/cmath:468:44: error: __builtin_types_compatible_p
is not valid in C++ __capture_fpclassify(_Tp __f) { return
fpclassify(__f); } ^~~~~~~~~~~~~~~
/usr/include/math.h:104:2: note: expanded from macro 'fpclassify'
        __fp_type_select(x, __fpclassifyf, __fpclassifyd, __fpclassifyl)
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/math.h:91:2: note: expanded from macro '__fp_type_select'
        __builtin_types_compatible_p(__typeof(x), long double),
        ld(x),


[...]

I was wondering why /usr/include/c++/4.2/cmath gets included and not
the header provided for CLANG. I guess this is a typo/bug. I did do dig
deeper into it.

Hope someone can fix this.

Regards,
Oliver