add support for Blackfin symbol prefixes to examples

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/blackfin_config.mk b/blackfin_config.mk
index beb9498..e91318e 100644
--- a/blackfin_config.mk
+++ b/blackfin_config.mk
@@ -23,3 +23,5 @@
 
 PLATFORM_RELFLAGS += -ffixed-P5
 PLATFORM_CPPFLAGS += -DCONFIG_BLACKFIN
+
+SYM_PREFIX = _