blkid,ext2fs: avoid name clash with __u{8,16,32,64}

blkid,ext2fs: avoid name clash with __u{8,16,32,64}

Try to avoid name clashes with definitions of __u8, __u16, __u32,
and __u64 in userspace, in case other headers also define these
types.  Define HAVE___{S,U}{8,16,32,64} preprocessor macros to
show that these types are already defined.

This would avoid the need to check for _BLKID_TYPES_H in ext2_types.h
and _EXT2_TYPES_H in blkid_types.h, but since older versions of these
headers did not use HAVE___U8 et.al. keep these checks around for now.

Report an error if there are no 64-bit types available.  The code
will not compile if these are not available.

Signed-off-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>