diff -up tkimg1.4/libpng/pngtclDecls.h.gcc10 tkimg1.4/libpng/pngtclDecls.h
--- tkimg1.4/libpng/pngtclDecls.h.gcc10	2020-01-31 17:40:40.391470848 -0500
+++ tkimg1.4/libpng/pngtclDecls.h	2020-01-31 17:40:45.791358236 -0500
@@ -1104,7 +1104,7 @@ typedef struct PngtclStubs {
 #ifdef __cplusplus
 extern "C" {
 #endif
-PNG_IMPEXP const PngtclStubs *pngtclStubsPtr;
+extern PNG_IMPEXP const PngtclStubs *pngtclStubsPtr;
 #ifdef __cplusplus
 }
 #endif