Fix 32-bit bionic toybox build.

Change-Id: Ief60448ec3dddf88e0202fafaefa3c79462a3e70
diff --git a/lib/portability.h b/lib/portability.h
index f83cab6..ff22fa5 100644
--- a/lib/portability.h
+++ b/lib/portability.h
@@ -79,7 +79,7 @@
 // correct name to the broken name.
 
 char *dirname(char *path);
-char *__xpg_basename (char *path);
+char *__xpg_basename(char *path);
 static inline char *basename(char *path) { return __xpg_basename(path); }
 
 // uClibc pretends to be glibc and copied a lot of its bugs, but has a few more
@@ -154,11 +154,19 @@
 
 #endif // glibc in general
 
-#ifndef __GLIBC__
+#if !defined(__GLIBC__) && !defined(__BIONIC__)
 // POSIX basename.
 #include <libgen.h>
 #endif
 
+// glibc was handled above; for 32-bit bionic we need to avoid a collision
+// with toybox's basename_r so we can't include <libgen.h> even though that
+// would give us a POSIX basename(3).
+#if defined(__BIONIC__)
+char *basename(char *path);
+char *dirname(char *path);
+#endif
+
 // Work out how to do endianness
 
 #ifndef __APPLE__