Using libcxx with musl's math.h

[Jeroen Ketema <jeroen@codeplay.com>]

Hello,

I'm trying to use libcxx's cmath header together with musl's math.h. 
However this currently fails, because libcxx expects certain symbols to 
be functions, while musl defines them as macros. For example (compiling 
with clang):

cmath:309:9: error: no member named 'signbit' in the global
       namespace; did you mean '__signbit'?
using ::signbit;
       ~~^

where signbit is a macro in musl, but where libcxx expects it to be a 
function.

My question is: what would be the proper way to fix this? The main issue 
being of course that I cannot simply define signbit to be a function, 
because it requires a form of overloading.

Thanks,

  Jeroen