The command you need is:
# diff -ruP libsmbios-0.10.0_beta5 libsmbios-0.10.0_beta5_SENTHIL
Where the libsmbios-0.10.0_beta5_SENTHIL/ directory has your
modifications. Make sure that you run a "make distclean" in both
directories and look at the patch to ensure no stray files got in.
After this, go ahead and send it as an attachment. Doing the patch
inline is excellent for reviewing, but because of the line-wraps your
email client puts in, it is not possible to apply it this way.