Fix compilation error in archiver/pax under cygwin

[kflu]

Building archiver/pax under cygwin would give error:

/usr/lib/gcc/x86_64-pc-cygwin/11/../../../../x86_64-pc-cygwin/bin/ld:
ar_subs.o:ar_subs.c:(.bss+0x24d8): multiple definition of `chdname';
ar_io.o:ar_io.c:(.bss+0x20): first defined here
...

Full error log: https://ttm.sh/WPc.txt

The patch basically changed the initialization of global variable chdname from extern.h to options.c