send_sig and library question

[Bug Hunter]

  I need to use send_sig from an application.  It is not in the man pages.
It is not in the info pages.

  It is in the kernel source.  How do I find the library that send_sig is
currently in so that I can link to it?  On a more general level, how do I
find the library any function I am interested in is in?

bug