[libc++] Patch: build regression

["C. Bergström"]

I realize this commit fixes an issue and that before it wasn't correct 
c++11. The problem is that it created a build regression (below)
https://github.com/llvm-mirror/libcxx/commit/854a7a02b4bf2d73735559003e3c4abfda2b209f 


This "hacky" patch is the best I've got to offer..
https://gist.github.com/erdizz/9257a34c7ef2c0682060

It produces with gcc-4.7 (4.8 not tested, but I don't expect any difference)
---------

SLES build host includes this
--------------------
/*
/* Return nonzero if VALUE is not a number.  */
__MATHDECL_1 (int,isnan,, (_Mdouble_ __value)) __attribute__ ((__const__));

/* Bessel functions.  */
__MATHCALL (j0,, (_Mdouble_));
__MATHCALL (j1,, (_Mdouble_));
__MATHCALL (jn,, (int, _Mdouble_));
__MATHCALL (y0,, (_Mdouble_));
__MATHCALL (y1,, (_Mdouble_));
__MATHCALL (yn,, (int, _Mdouble_));
*/


Error
----------------
In file included from 
/root/bamboo-agent-home/xml-data/build-dir/NIGHTLYLINUX-DEBUG/src/libcxx/src/random.cpp:16:
In file included from 
/root/bamboo-agent-home/xml-data/build-dir/NIGHTLYLINUX-DEBUG/src/libcxx/include/random:1647:
/root/bamboo-agent-home/xml-data/build-dir/NIGHTLYLINUX-DEBUG/src/libcxx/include/cmath:431:1: 
error: functions that differ only in their return type cannot be overloaded
isnan(double __x) _NOEXCEPT
^
/usr/include/bits/mathcalls.h:235:19: note: previous declaration is here
__MATHDECL_1 (int,isnan,, (_Mdouble_ __value)) __attribute__ ((__const__));
                   ^
/usr/include/math.h:65:31: note: expanded from macro '__MATHDECL_1'
   extern type __MATH_PRECNAME(function,suffix) args __THROW
                               ^
/usr/include/math.h:68:42: note: expanded from macro '__MATH_PRECNAME'
#define __MATH_PRECNAME(name,r) __CONCAT(name,r)
                                          ^
/usr/include/sys/cdefs.h:80:23: note: expanded from macro '__CONCAT'
#define __CONCAT(x,y)   x ## y
                         ^
1 error generated.
gmake[5]: *** [lib/CMakeFiles/cxx.dir/__/src/random.cpp.o] Error 1
gmake[4]: *** [lib/CMakeFiles/cxx.dir/all] Error 2
gmake[3]: *** [all] Error 2