rename dynamic linker _start to _dlstart in the stub version

the renaming was previously applied to all real versions of the
function in commit 3fa2eb2aba8d6b54dec53e7ad4c37e17392b166f.

src/ldso/start.c

@@ -2,7 +2,7 @@
 
 /* stub for archs that lack dynamic linker support */
 
-void _start()
+void _dlstart()
 {
 	_Exit(1);
 }