compiling ArcticFox on 10.11 - atomic not found, cxx11

[Riccardo Mottola]

Hi,

I have issues compiling ArcticFox on 10.11. I think I have some issues 
with compilers and C++ versions.
I got a used macbook since the other one with 10.13 has a fried GPU ans 
inconvenient to use.

On 10.7, where I regularly build, I can use MacPorts clang 6 without any 
issues or additional parameters.
On 10.13, I can build with apple clang, but had issues with MP clang's I 
was still investigating.

On 10.11 I cannot get it to build in any condition.
Whether I use apple's clang or MacPorts clang, I get an issue with 
atomics not being found, I tired clang6 (known to work on older 10.7) 
and 9. -std=c++11 should help fixing the atoimc issue, but apparently it 
doesn't

I configure:
export CC="clang-mp-9.0 -march=core2 -mtune=core2"
export CXX="clang++-mp-9.0 -march=core2 -mtune=core2 -std=c++11"

Build then fails with:

188:52.94 
/Users/multix/Documents/code/Arctic-Fox/media/gmp-clearkey/0.1/RefCounted.h:21:10: 
fatal error: 'atomic' file not found
188:52.94 #include <atomic>
188:52.94          ^~~~~~~~
188:52.94 1 error generated.
188:52.94



any hints? Strange that if it is a old c++ version, on 10.7 I had no 
issues...

Riccardo