adb: use sys/uio.h for iovec operations

readv/writev and struct iovec are declared in sys/uio.h per POSIX.
using it without sys/uio.h is a GNU extension.

ref #10794

src/adb.c

@@ -5,6 +5,7 @@
 #include <errno.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
+#include <sys/uio.h>
 #include <openssl/pem.h>
 #include <openssl/err.h>