add getauxval function

in a sense this implementation is incomplete since it doesn't provide
the HWCAP_* macros for use with AT_HWCAP, which is perhaps the most
important intended usage case for getauxval. they will be added at a
later time.

include/sys/auxv.h

@@ -0,0 +1,16 @@
+#ifndef _SYS_AUXV_H
+#define _SYS_AUXV_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <elf.h>
+
+unsigned long getauxval(unsigned long);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif