ldso: bfin: add alias from __start to _start

On Blackfin systems, we have underscore prefixes in our ABI.  So instead
of _start, we use __start.  However, the makefile explicitly sets _start
as the entry point to support toolchains that implicitly use other symbols
as the default entry.  It's easy enough to add a hidden alias in the
Blackfin code for free to support this.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

ldso/ldso/bfin/dl-startup.h

@@ -40,6 +40,10 @@ __asm__(
 	"	.text\n"
 	"	.global	__start\n"
 	"	.type	__start,@function\n"
+	/* Build system expects a "_start" for the entry point;
+	   provide it as it's free to do so with aliases.  */
+	"	.set	_start, __start\n"
+	"	.global	_start\n"
 	"__start:\n"
 	"	call	.Lcall\n"
 	".Lcall:\n"