[LyX/master] Fix deprecation warning

[Juergen Spitzmueller]

commit cba24bb642606bbb8c890b21e799d9f225ad9a3d
Author: Juergen Spitzmueller <spitz at lyx.org>
Date:   Sat Aug 15 16:06:56 2020 +0200

    Fix deprecation warning
---
 src/frontends/qt/GuiAbout.cpp |   23 +++++++++++++++++++----
 1 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/src/frontends/qt/GuiAbout.cpp b/src/frontends/qt/GuiAbout.cpp
index 3c874df..8e720df 100644
--- a/src/frontends/qt/GuiAbout.cpp
+++ b/src/frontends/qt/GuiAbout.cpp
@@ -203,12 +203,27 @@ static QString buildinfo()
 	QString res;
 	QTextStream out(&res);
 	out << "LyX " << lyx_version
-		<< " (" << lyx_release_date << ")" << endl;
+		<< " (" << lyx_release_date << ")"
+#if (QT_VERSION >= QT_VERSION_CHECK(5, 15, 0))
+		<< Qt::endl;
+#else
+		<< endl;
+#endif
 	if (std::string(lyx_git_commit_hash) != "none")
 		out << qt_("  Git commit hash ")
-		    << QString(lyx_git_commit_hash).left(8) << endl;
-
-	out << lyx_version_info << endl;
+		    << QString(lyx_git_commit_hash).left(8)
+#if (QT_VERSION >= QT_VERSION_CHECK(5, 15, 0))
+		    << Qt::endl;
+#else
+		    << endl;
+#endif
+
+	out << lyx_version_info 
+#if (QT_VERSION >= QT_VERSION_CHECK(5, 15, 0))
+	    << Qt::endl;
+#else
+	    << endl;
+#endif
 	return res;
 }