Front-end: allow max size built-in arrays like gl_ClipDistance

Fixed off-by-one error with gl_MaxClipDistances and similar limits.

Test/maxClipDistances.vert

@@ -0,0 +1,7 @@
+#version 130
+
+out float gl_ClipDistance[8];	// OK, 8 is gl_MaxClipDistances
+
+void main()
+{
+}