Fix debug build

src/hb-open-type-private.hh

diff --git a/src/hb-open-type-private.hh b/src/hb-open-type-private.hh
index 836a98f..9977a6e 100644
--- a/src/hb-open-type-private.hh
+++ b/src/hb-open-type-private.hh
@@ -125,7 +125,7 @@
 	HB_STMT_START { \
 	    if (sanitize_depth < HB_DEBUG_SANITIZE) \
 		fprintf (stderr, "SANITIZE(%p) %-*d-> %s\n", \
-			 (CONST_CHARP (this) == NullPool) ? 0 : this, \
+			 (CONST_CHARP (this) == CONST_CHARP (&NullPool)) ? 0 : this, \
 			 sanitize_depth, sanitize_depth, \
 			 __PRETTY_FUNCTION__); \
 	} HB_STMT_END

src/hb-ot-layout-gsubgpos-private.hh

diff --git a/src/hb-ot-layout-gsubgpos-private.hh b/src/hb-ot-layout-gsubgpos-private.hh
index 43f3d75..4561aa3 100644
--- a/src/hb-ot-layout-gsubgpos-private.hh
+++ b/src/hb-ot-layout-gsubgpos-private.hh
@@ -44,7 +44,7 @@
 	HB_STMT_START { \
 	    if (apply_depth < HB_DEBUG_APPLY) \
 		fprintf (stderr, "APPLY(%p) %-*d-> %s\n", \
-			 (CONST_CHARP (this) == NullPool) ? 0 : this, \
+			 (CONST_CHARP (this) == CONST_CHARP (&NullPool)) ? 0 : this, \
 			 apply_depth, apply_depth, \
 			 __PRETTY_FUNCTION__); \
 	} HB_STMT_END