osdep: Create qemu_getauxval and qemu_init_auxval

Abstract away dependence on a system implementation of getauxval.

Signed-off-by: Richard Henderson <rth@twiddle.net>
diff --git a/vl.c b/vl.c
index 8d5d874..0c9c359 100644
--- a/vl.c
+++ b/vl.c
@@ -2894,6 +2894,7 @@
     init_clocks();
     rtc_clock = QEMU_CLOCK_HOST;
 
+    qemu_init_auxval(envp);
     qemu_cache_utils_init(envp);
 
     QLIST_INIT (&vm_change_state_head);