Use literal bools when possible rather than ints.

src/hb-buffer-verify.cc

@@ -149,7 +149,7 @@ buffer_verify_unsafe_to_break (hb_buffer_t  *buffer,
     }
     assert (text_start < text_end);
 
-    if (0)
+    if (false)
       printf("start %u end %u text start %u end %u\n", start, end, text_start, text_end);
 
     hb_buffer_clear_contents (fragment);
@@ -288,7 +288,7 @@ buffer_verify_unsafe_to_concat (hb_buffer_t        *buffer,
       }
       assert (text_start < text_end);
 
-      if (0)
+      if (false)
 	printf("start %u end %u text start %u end %u\n", start, end, text_start, text_end);
 
 #if 0

src/hb-ot-cmap-table.hh

@@ -1979,7 +1979,7 @@ struct cmap
 			    hb_codepoint_t *glyph,
 			    cache_t *cache = nullptr) const
     {
-      if (unlikely (!this->get_glyph_funcZ)) return 0;
+      if (unlikely (!this->get_glyph_funcZ)) return false;
       return _cached_get (unicode, glyph, cache);
     }
 

src/hb-ot-stat-table.hh

@@ -357,7 +357,7 @@ struct AxisValue
     case 2: return u.format2.get_value ();
     case 3: return u.format3.get_value ();
     case 4: return u.format4.get_axis_record (axis_index).get_value ();
-    default:return 0;
+    default:return false;
     }
   }