hellorina: fix build of [file] on Debian 8

software/hellorina/software.cfg

@@ -6,6 +6,14 @@ parts =
     slapos-cookbook
     template
 
+[file]
+# For old GCC like 4.9.2 on Debian 8.
+# XXX: This should be moved to component/rina-tools/buildout.cfg, next to where
+#      we force use of system GCC. However, our buildout patches are still not
+#      perfect concerning the processing of +=
+environment +=
+  CFLAGS=-std=c99 -g -O2
+
 [template]
 recipe = slapos.recipe.template:jinja2
 template = ${:_profile_base_location_}/instance.cfg.in