diff -burN  qt-everywhere-src-5.14.1/qttools/src/assistant/assistant/assistant.pro qt-everywhere-src-5.14.1_orig/qttools/src/assistant/assistant/assistant.pro
--- qt-everywhere-src-5.14.1/qttools/src/assistant/assistant/assistant.pro	2020-01-17 06:51:13.000000000 +0100
+++ qt-everywhere-src-5.14.1_orig/qttools/src/assistant/assistant/assistant.pro	2020-08-24 15:19:57.044203325 +0200
@@ -45,6 +45,8 @@
     openpagesmanager.h \
     openpagesswitcher.h
 
+LIBS += -lpng
+
 SOURCES += aboutdialog.cpp \
     bookmarkdialog.cpp \
     bookmarkfiltermodel.cpp \

--- qt-everywhere-src-5.14.1/qttools/src/assistant/qhelpgenerator/qhelpgenerator.pro	2020-01-17 06:51:13.000000000 +0100
+++ qt-everywhere-src-5.14.1_orig/qttools/src/assistant/qhelpgenerator/qhelpgenerator.pro	2020-08-24 15:42:12.924236449 +0200
@@ -15,5 +15,7 @@
            qhelpprojectdata_p.h \
            qhelpdatainterface_p.h
 
+LIBS += -lpng
+
 QMAKE_TARGET_DESCRIPTION = "Qt Compressed Help File Generator"
 load(qt_tool)

--- qt-everywhere-src-5.14.1/qttools/src/designer/src/designer/designer.pro	2020-01-17 06:51:13.000000000 +0100
+++ qt-everywhere-src-5.14.1_orig/qttools/src/designer/src/designer/designer.pro	2020-08-24 15:44:13.892239448 +0200
@@ -53,6 +53,8 @@
     assistantclient.cpp \
     mainwindow.cpp
 
+LIBS += -lpng
+
 PRECOMPILED_HEADER=qdesigner_pch.h
 
 FORMS += saveformastemplate.ui \

--- qt-everywhere-src-5.14.1/qttools/src/pixeltool/pixeltool.pro	2020-01-17 06:51:13.000000000 +0100
+++ qt-everywhere-src-5.14.1_orig/qttools/src/pixeltool/pixeltool.pro	2020-08-24 15:45:42.572241647 +0200
@@ -6,5 +6,6 @@
 
 SOURCES += main.cpp qpixeltool.cpp
 HEADERS += qpixeltool.h
+LIBS += -lpng
 
 load(qt_app)

--- qt-everywhere-src-5.14.1/qttools/src/linguist/linguist/linguist.pro	2020-01-17 06:51:13.000000000 +0100
+++ qt-everywhere-src-5.14.1_orig/qttools/src/linguist/linguist/linguist.pro	2020-08-24 15:59:27.476262101 +0200
@@ -55,6 +55,8 @@
     translationsettingsdialog.h \
     ../shared/simtexth.h
 
+LIBS += -lpng
+
 contains(QT_PRODUCT, OpenSource.*):DEFINES *= QT_OPENSOURCE
 DEFINES += QT_KEYWORDS
 TARGET = linguist

--- qt-everywhere-src-5.14.1/qttools/src/qtdiag/qtdiag.pro	2020-01-17 06:51:13.000000000 +0100
+++ qt-everywhere-src-5.14.1_orig/qttools/src/qtdiag/qtdiag.pro	2020-08-24 15:52:35.732251892 +0200
@@ -10,5 +10,6 @@
 
 SOURCES += main.cpp qtdiag.cpp
 HEADERS += qtdiag.h
+LIBS += -lpng
 
 load(qt_app)

--- qt-everywhere-src-5.11.3-orig/qttools/src/assistant/qcollectiongenerator/qcollectiongenerator.pro   2018-11-23 08:41:24.000000000 +0100
+++ qt-everywhere-src-5.11.3/qttools/src/assistant/qcollectiongenerator/qcollectiongenerator.pro    2020-09-04 15:42:48.968480227 +0200
@@ -1,5 +1,8 @@
 QT += network help-private
 TARGET = qcollectiongenerator
+
+LIBS += -lpng
+
 SOURCES += ../shared/helpgenerator.cpp \
     main.cpp \
     ../shared/collectionconfiguration.cpp

--- qt-everywhere-src-5.11.3-orig/qttools/src/assistant/qhelpconverter/qhelpconverter.pro   2018-11-23 08:41:24.000000000 +0100
+++ qt-everywhere-src-5.11.3/qttools/src/assistant/qhelpconverter/qhelpconverter.pro    2020-09-04 15:48:05.003811338 +0200
@@ -1,5 +1,7 @@
 QT += help widgets
 
+LIBS += -lpng
+
 SOURCES += conversionwizard.cpp \
            inputpage.cpp \
            generalpage.cpp \
