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