fdisk: fix to build for IA32

fdisk: fix to build for IA32

Tested architectures:
- i486 using gcc -march=i486
- i586 using gcc -march=pentium-mmx
- i686 using gcc -march={pentiumpro,pentium2,pentium3,pentium-m,pentium4}

Without this fix building fdisk fails for for all tested arch/cpu types
emiting following error:
------------------------------------------------------------------------------
In file included from fdiskbsdlabel.c:62:0:
fdiskbsdlabel.h:61:2: error: #error unknown architecture
fdiskbsdlabel.c: In function 'bselect':
fdiskbsdlabel.c:180:44: error: 'BSD_LABELSECTOR' undeclared (first use in this function)
fdiskbsdlabel.c:180:44: note: each undeclared identifier is reported only once for each function it appears in
fdiskbsdlabel.c: In function 'xbsd_write_bootstrap':
fdiskbsdlabel.c:539:24: error: 'BSD_LABELSECTOR' undeclared (first use in this function)
fdiskbsdlabel.c: In function 'xbsd_readlabel':
fdiskbsdlabel.c:744:28: error: 'BSD_LABELSECTOR' undeclared (first use in this function)
fdiskbsdlabel.c:744:60: error: 'BSD_LABELOFFSET' undeclared (first use in this function)
fdiskbsdlabel.c: In function 'xbsd_writelabel':
fdiskbsdlabel.c:769:32: error: 'BSD_LABELSECTOR' undeclared (first use in this function)
fdiskbsdlabel.c:780:61: error: 'BSD_LABELOFFSET' undeclared (first use in this function)
make[2]: *** [fdisk-fdiskbsdlabel.o] Error 1
------------------------------------------------------------------------------

This fix was tested with following major toolchain components:

binutils 2.21.53.0.2
gcc 4.6.2
glibc 2.14.1