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

libc/include/elf.h

@@ -28,8 +28,23 @@
 #ifndef _ELF_H
 #define _ELF_H
 
+#include <stdint.h>
 #include <linux/auxvec.h>
 #include <sys/exec_elf.h>
 
+typedef struct {
+  uint32_t a_type;
+  union {
+    uint32_t a_val;
+  } a_un;
+} Elf32_auxv_t;
+
+typedef struct {
+  uint64_t a_type;
+  union {
+    uint64_t a_val;
+  } a_un;
+} Elf64_auxv_t;
+
 #endif /* _ELF_H */