move calls to application init functions after crt1 entry point

this change is needed to be compatible with fdpic, where some of the
main application's relocations may be performed as part of the crt1
entry point. if we call init functions before passing control, these
relocations will not yet have been performed, and the init code will
potentially make use of invalid pointers.

conceptually, no code provided by the application or third-party
libraries should run before the application entry point. the
difference is not observable to programs using the crt1 we provide,
but it could come into play if custom entry point code is used, so
it's better to be doing this right anyway.

src/env/__libc_start_main.c

@@ -67,6 +67,9 @@ int __libc_start_main(int (*main)(int,char **,char **), int argc, char **argv)
 	uintptr_t a = (uintptr_t)&__init_array_start;
 	for (; a<(uintptr_t)&__init_array_end; a+=sizeof(void(*)()))
 		(*(void (**)())a)();
+#else
+	void __libc_start_init(void);
+	__libc_start_init();
 #endif
 
 	/* Pass control to the application */

src/ldso/dynlink.c

@@ -1203,6 +1203,11 @@ static void do_init_fini(struct dso *p)
 	if (need_locking) pthread_mutex_unlock(&init_fini_lock);
 }
 
+void __libc_start_init(void)
+{
+	do_init_fini(tail);
+}
+
 static void dl_debug_state(void)
 {
 }
@@ -1630,7 +1635,6 @@ _Noreturn void __dls3(size_t *sp)
 	__init_libc(envp, argv[0]);
 	atexit(do_fini);
 	errno = 0;
-	do_init_fini(tail);
 
 	CRTJMP((void *)aux[AT_ENTRY], argv-1);
 	for(;;);