arm64 compile _seems_ to have worked with Macports GCC-12

[jonCAstickel]

This is more of a comment than an issue. I use Macports rather than Homebrew on my Mac with an M2 cpu. Macports installed GCC (gcc-12) does not have the capability to compile x86-64, only arm64. So I tried it, and it seems to have worked! I used:

port select gcc mp-gcc12
cmake .. -DCMAKE_BUILD_TYPE=Release
cmake --build .

Then in iPython:

In [1]: from CoolProp import CoolProp

In [2]: CoolProp.PropsSI("T","P",101325,"Q",0,"REFPROP::Water")
Out[2]: 373.1242958476957

I could make a PR to update the Mac section of the README if you like.

[ianhbell]

I'm not sure that really requires an update to docs, but you can open and PR and I can review it if you like