pdisk: use strerror()

Use strerror().
pdisk: include stdlib.h on Linux

Include stdlib.h on Linux to avoid compilation warnings.
pdisk: delete kernel-defs.h

Delete kernel-defs.h.
pdisk: fix bitfield data type to 32-bits

Fix bitfield data type to 32-bits.
pdisk: include string.h

Include string.h to avoid compilation warnings.
pdisk: include fcntl.h

Include fcntl.h to avoid compilation warnings.
pdisk: delete unused variables

Delete unused variables.
pdisk: fix printf() format strings

Fix printf() format strings.
pdisk: fix array initializer

Fix array initializer.
pdisk: define _LARGEFILE64_SOURCE

Define _LARGEFILE64_SOURCE.
pdisk: include unistd.h on Linux

Include unistd.h to avoid compilation warnings.
pdisk: set CFLAGS

Set some default CFLAGS.