rpm -ba doesn't work because we don't have a "real" source distro

diff --git a/Makefile b/Makefile
index fb1c597..1bbcc4e 100644
--- a/Makefile
+++ b/Makefile
@@ -10,7 +10,7 @@
 
 .PHONY: rpm
 rpm: klibc.spec
-	+$(rpmbuild) -ba klibc.spec
+	+$(rpmbuild) -bb klibc.spec
 
 %:
 	@set -e; for d in $(SUBDIRS); do $(MAKE) -C $$d $@; done