[LyX/master] Fixup 6bbd88ac: compilation fix for Qt4

[Jean-Marc Lasgouttes]

commit 69834f1e0da4dc09007f0947b870fd66a72501e3
Author: Jean-Marc Lasgouttes <lasgouttes at lyx.org>
Date:   Mon Sep 27 13:56:04 2021 +0200

    Fixup 6bbd88ac: compilation fix for Qt4
---
 src/frontends/qt/GuiFontMetrics.cpp |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/src/frontends/qt/GuiFontMetrics.cpp b/src/frontends/qt/GuiFontMetrics.cpp
index 8273ed8..5e8f535 100644
--- a/src/frontends/qt/GuiFontMetrics.cpp
+++ b/src/frontends/qt/GuiFontMetrics.cpp
@@ -57,6 +57,15 @@ using namespace lyx::support;
 #  error "Define at least one of BIDI_USE_OVERRIDE or BIDI_USE_FLAG"
 #endif
 
+
+#if QT_VERSION < 0x050000
+inline uint qHash(double key)
+{
+	return qHash(QByteArray(reinterpret_cast<char const *>(&key), sizeof(key)));
+}
+#endif
+
+
 namespace std {
 
 /*