[BUG] Build fails on macOS due to Linux-specific header: `mya.c: fatal error: 'argp.h' file not found`

## Bug Description
```
[ 50%] Building C object CMakeFiles/mya.dir/src/mya.c.o
/opt/local/bin/ccache /usr/bin/clang -I/opt/local/var/macports/build/myanimelist-cli-05909388/work/myanimelist-cli-e2a274d3128397309c1b24c5116d3021b9f03248/include -pipe -Os -DNDEBUG -I/opt/local/include -isysroot/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk -g -Wall -std=gnu11 -arch x86_64 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk -mmacosx-version-min=10.15 -MD -MT CMakeFiles/mya.dir/src/mya.c.o -MF CMakeFiles/mya.dir/src/mya.c.o.d -o CMakeFiles/mya.dir/src/mya.c.o -c /opt/local/var/macports/build/myanimelist-cli-05909388/work/myanimelist-cli-e2a274d3128397309c1b24c5116d3021b9f03248/src/mya.c
/opt/local/var/macports/build/myanimelist-cli-05909388/work/myanimelist-cli-e2a274d3128397309c1b24c5116d3021b9f03248/src/mya.c:4:10: fatal error: 'argp.h' file not found
#include
^~~~~~~~
1 error generated.
make[2]: *** [CMakeFiles/mya.dir/src/mya.c.o] Error 1
```

## Expected Behavior
The build should succeed.

## Environment
Operating System: macOS Catalina
CMake

Start by reproducing the macOS build and inspecting the argp.h include in src/mya.c, then review the CMake build configuration for platform-specific handling. The work is done when the project builds successfully on macOS Catalina without the reported missing-header error.

Written by the indexing model from the issue text.