libc: add getauxval()

libc: add getauxval()

Add support for getauxval().  This method allows a program an easy way
to retrieve information from the kernel auxiliary vector, and will
hopefully replace other clumsy ways of accessing this same information.

This particular function was also added to glibc in glibc 2.16.
See the following URLs for more details.

  * http://lwn.net/Articles/519085/
  * http://www.gnu.org/software/libc/manual/html_node/Auxiliary-Vector.html

This change is a prerequisite for bug 7959813.

Bug: http://code.google.com/p/android/issues/detail?id=38441
Change-Id: Iba19d899df334bddc6f4899077ece2fc87564ea8