make _dlstart_c function use hidden visibility

otherwise the call/jump from the crt_arch.h asm may not resolve
correctly without -Bsymbolic-functions.

src/ldso/dlstart.c

@@ -9,6 +9,7 @@
 
 #include "crt_arch.h"
 
+__attribute__((__visibility__("hidden")))
 void _dlstart_c(size_t *sp, size_t *dynv)
 {
 	size_t i, aux[AUX_CNT], dyn[DYN_CNT];