$ ./stat-size-test.exe $HOME/foo /cygdrive/z/foo
/home/jonathan/foo: fstat: st_size=12
/home/jonathan/foo: stat: st_size=12
/cygdrive/z/foo: fstat: st_size=0
/cygdrive/z/foo: stat: st_size=12

$ mount
C:/cygwin64/bin on /usr/bin type ntfs (binary,auto)
C:/cygwin64/lib on /usr/lib type ntfs (binary,auto)
C:/cygwin64 on / type ntfs (binary,auto)
C: on /cygdrive/c type ntfs (binary,posix=0,user,noumount,auto)
D: on /cygdrive/d type iso9660 (binary,posix=0,user,noumount,auto)
S: on /cygdrive/s type ntfs (binary,posix=0,user,noumount,auto)
U: on /cygdrive/u type ntfs (binary,posix=0,user,noumount,auto)
Z: on /cygdrive/z type prlsf (binary,posix=0,user,noumount,auto)