cmd/zpool and lib/libzutil Makefile's use -I., which won't work with a
VPATH build. Replace it with -I$(srcdir) instead.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Closes#10379Closes#10421