support macos

So far, here are steps we might need to do to support Mac

1. Install XQuartz https://www.xquartz.org/
1. Also install linux packages
1. brew install coreutils
1. brew install llvm (takes forever)
1. ln -s "$(brew --prefix llvm)/bin/clang-format" "/usr/local/bin/clang-format"
1. ln -s "$(brew --prefix llvm)/bin/clang-tidy" "/usr/local/bin/clang-tidy"
1. Install googletest
git clone https://github.com/google/googletest
cd googletest
mkdir build
cd build
cmake .. -DCMAKE_CXX_STANDARD=17
make
make install
1. Change makefiles. Can we add/remove flags depending on the OS? Add these for Mac but not for Linux?
1. Compilation: add ```-lm -I/opt/X11/include -lpthread -lX11 -lstdc++ -I/usr/X11R6/include -L/usr/X11R6/lib```
1. unittest: add ```-lm -lpthread -lX11 -I/usr/X11R6/include -L/usr/X11R6/lib```

Start by reviewing the repository's makefiles and the existing compilation and unittest targets, then compare their Linux assumptions with the listed macOS dependencies and flags. Verify the XQuartz, Homebrew, LLVM, and GoogleTest setup described in the issue. Done means the project builds and its unit tests run on macOS without breaking the Linux build.

Written by the indexing model from the issue text.