[klibc] <sys/auxv.h>: add missing dependency <klibc/extern.h>

__extern is defined in <klibc/extern.h>

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
diff --git a/usr/include/sys/auxv.h b/usr/include/sys/auxv.h
index 08fcfcf..fc98ed4 100644
--- a/usr/include/sys/auxv.h
+++ b/usr/include/sys/auxv.h
@@ -2,6 +2,7 @@
 #define _SYS_AUXV_H
 
 #include <klibc/compiler.h>
+#include <klibc/extern.h>
 #include <elf.h>
 
 #define _AUXVAL_MAX	AT_SYSINFO_EHDR