e2fsprogs: add (optional) sparse checking to the build

e2fsprogs: add (optional) sparse checking to the build

Run sparse against source files when building e2fsprogs with 'make C=1'.  If
instead C=2, it configures basic ext2 types for bitwise checking with sparse,
which can help find the (many many) spots where conversion errors are
(possibly) happening.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>