[config] Add HB_NO_VAR to disable variations support, enabled by HB_TINY

Part of https://github.com/harfbuzz/harfbuzz/issues/1652
diff --git a/src/hb-ot-layout-gsubgpos.hh b/src/hb-ot-layout-gsubgpos.hh
index 4bc3d7e..dd54c9b 100644
--- a/src/hb-ot-layout-gsubgpos.hh
+++ b/src/hb-ot-layout-gsubgpos.hh
@@ -2661,11 +2661,17 @@
 
   bool find_variations_index (const int *coords, unsigned int num_coords,
 			      unsigned int *index) const
-  { return (version.to_int () >= 0x00010001u ? this+featureVars : Null(FeatureVariations))
-	   .find_index (coords, num_coords, index); }
+  {
+#ifdef HB_NOVAR
+    return false;
+#endif
+    return (version.to_int () >= 0x00010001u ? this+featureVars : Null(FeatureVariations))
+	    .find_index (coords, num_coords, index);
+  }
   const Feature& get_feature_variation (unsigned int feature_index,
 					unsigned int variations_index) const
   {
+#ifndef HB_NO_VAR
     if (FeatureVariations::NOT_FOUND_INDEX != variations_index &&
 	version.to_int () >= 0x00010001u)
     {
@@ -2674,6 +2680,7 @@
       if (feature)
 	return *feature;
     }
+#endif
     return get_feature (feature_index);
   }
 
@@ -2695,8 +2702,10 @@
 			 this,
 			 out);
 
+#ifndef HB_NO_VAR
     if (version.to_int () >= 0x00010001u)
      out->featureVars.serialize_copy (c->serializer, featureVars, this, out);
+#endif
 
     return_trace (true);
   }
@@ -2717,7 +2726,10 @@
 		  scriptList.sanitize (c, this) &&
 		  featureList.sanitize (c, this) &&
 		  CastR<OffsetTo<TLookupList>> (lookupList).sanitize (c, this) &&
-		  (version.to_int () < 0x00010001u || featureVars.sanitize (c, this)));
+#ifndef HB_NO_VAR
+		  (version.to_int () < 0x00010001u || featureVars.sanitize (c, this)) &&
+#endif
+		  true);
   }
 
   template <typename T>