For musl libc declare a macro version of basename(3).

--- a/src/core/sysfs.cc	2016-05-07 05:36:45.771620396 +0200
+++ b/src/core/sysfs.cc	2016-05-07 05:37:33.265617827 +0200
@@ -19,6 +19,10 @@
 
 __ID("@(#) $Id$");
 
+#if !defined(__GLIBC__)
+#define basename(src) (strrchr(src,'/') ? strrchr(src,'/')+1 : src)
+#endif
+
 using namespace sysfs;
 
 struct sysfs::entry_i
