Before you do anything else, you should read the FAQ at http://sourceware.org/glibc/wiki/FAQ. It answers common questions and describes problems you may experience with compilation and installation.
Features can be added to the GNU C Library via add-on bundles. These are
separate tar files, which you unpack into the top level of the source
tree. Then you give
configure the ‘--enable-add-ons’ option
to activate them, and they will be compiled into the library.
You will need recent versions of several GNU tools: definitely GCC and GNU Make, and possibly others. See Tools for Compilation, below.