Bidi: undef conflicting constants

On Solaris ES and CS are already defined, resulting in compilation
errors.  Since we won't need Solaris' ones here, simply undef them.

--- graphite2-1.2.0/src/Bidi.cpp
+++ graphite2-1.2.0/src/Bidi.cpp
@@ -30,6 +30,14 @@
 
 using namespace graphite2;
 
+/* Solaris' headers define these */
+#ifdef ES
+# undef ES
+#endif
+#ifdef CS
+# undef CS
+#endif
+
 enum DirCode {  // Hungarian: dirc
         Unk        = -1,
         N          =  0,   // other neutrals (default) - ON