Add QT5_CUSTOM_DIR as Qt root dir for install and lib subdirs

configure.in

@@ -3361,12 +3361,24 @@ libraries returned by 'pkg-config gtk+-2.0 --libs' or 'gtk-config
 
 
     if test "$wxUSE_QT" = 1; then
-        PKG_CHECK_MODULES(QT5,
-                          [Qt5Core Qt5Widgets Qt5Gui Qt5OpenGL Qt5Test],
-            [
         TOOLKIT=QT
         GUIDIST=QT_DIST
         TOOLKIT_DIR="qt"
+
+        if test -n "$QT5_CUSTOM_DIR" ; then
+            dnl the name of the directory where the files for this toolkit live
+            TOOLKIT_INCLUDE="${TOOLKIT_INCLUDE} -I${QT5_CUSTOM_DIR}/include"
+            GUI_TK_LIBRARY="${GUI_TK_LIBRARY} -L${QT5_CUSTOM_DIR}/lib \
+                            -lQt5Core -lQt5Widgets -lQt5Gui -lQt5OpenGL -lQt5Test \
+                            -Wl,-rpath,${QT5_CUSTOM_DIR}/lib"
+
+        elif test -z "$PKG_CONFIG" ; then
+            AC_MSG_ERROR([specify QT5_CUSTOM_DIR or make sure pkg-config is available to search for Qt5 libraries])
+
+        else
+            PKG_CHECK_MODULES(QT5,
+                          [Qt5Core Qt5Widgets Qt5Gui Qt5OpenGL Qt5Test],
+                [
                 TOOLKIT_INCLUDE="${TOOLKIT_INCLUDE} ${QT5_CFLAGS}"
                 GUI_TK_LIBRARY="${GUI_TK_LIBRARY} ${QT5_LIBS}"
                 if `pkg-config --variable qt_config Qt5Core | grep "reduce_relocations" >/dev/null`; then
@@ -3380,6 +3392,7 @@ libraries returned by 'pkg-config gtk+-2.0 --libs' or 'gtk-config
                 ]
             )
         fi
+    fi
     dnl the name of the directory where the files for this toolkit live
     TOOLKIT_DIR=`echo ${TOOLKIT} | tr '[[A-Z]]' '[[a-z]]'`
 

docs/qt/install.txt

@@ -91,6 +91,21 @@ cd tests
 make
 ./test_gui
 
+* Building wxQT, using qt-unified-XXX-online installer
+------------------------------------------------------
+
+Download qt-unified-XXX-online installer from the qt website.
+Install the Qt package of your choice (with the same minimum version
+restriction as above).
+The same build instructions apply, except that you need to explicitly pass
+to configure the Qt dir of the build intended to use as QT5_CUSTOM_DIR, i.e.
+
+# for Linux:
+../configure --with-qt --enable-debug QT5_CUSTOM_DIR=~/Qt/5.11.0/gcc_64
+
+# for Windows (ran from Git Bash, or any other Unix-like shell):
+../configure --with-qt --enable-debug QT5_CUSTOM_DIR=/c/Qt/5.11.0/mingw53_32
+
 * Building wxGT on Android
 --------------------------