If available, use qtchooser to select correct Qt tools

When the Qt directory is specified by --with-qt-dir, the tools
are only searched for in the corresponding bin subdir and their
full path is retained, so that it is not necessary modifying the
PATH and PKG_CONFIG_PATH environment variables to select a custom
Qt version. Otherwise, if qtchooser is detected early in the PATH,
the generic names are attempted with proper arguments to select the
desired Qt version (e.g., "moc -qt=qt5" if --enable-qt5 is specified).
Failing all of the above, the generic names with and without proper
suffixes (either -qt4 or -qt5) are checked in the PATH.
Eventually, a check is performed and a warning is issued if the
selected tools do not match the chosen Qt libraries.

config/qt4.m4

@@ -71,11 +71,20 @@ AC_DEFUN([QT_FIND_TOOL],
 	if test "x$USE_QT5" != "xno" ; then
 		qt_ext=qt5
 	fi
+
 	if test -n "$qt_cv_bin" ; then
 		AC_PATH_PROGS($1, [$2], [], $qt_cv_bin)
+	elif qtchooser -l 2>/dev/null | grep -q ^$qt_ext\$ >/dev/null ; then
+		AC_PATH_PROG(qtc_path, qtchooser, [], [$PATH])
+		AC_PATH_PROG($2_path, $2, [], [$PATH])
+		qtc_path=`dirname "$qtc_path"`
+		$2_path=`dirname "$$2_path"`
+		if test "$qtc_path" = "$$2_path" ; then
+			AC_CHECK_PROG($1, $2, [$2 -qt=$qt_ext],, [$PATH])
+		fi
 	fi
 	if test -z "$$1"; then
-		AC_PATH_PROGS($1, [$2-$qt_ext $2],[],$PATH)
+		AC_CHECK_PROGS($1, [$2-$qt_ext $2],[],$PATH)
 	fi
 	if test -z "$$1"; then
 		AC_MSG_ERROR([cannot find $2 binary.])

status.22x

@@ -40,6 +40,7 @@ What's new
 
 * BUILD/INSTALLATION
 
+- If available, use qtchooser to select correct Qt tools when configuring.