[LyX/master] Fix Clang warning about struct/class mismatch

[Scott Kostyshak]

commit 9649e80c44f501d3ec758343c2eb0fd53a47d10f
Author: Scott Kostyshak <skostysh at lyx.org>
Date:   Thu Nov 26 13:48:42 2020 -0500

    Fix Clang warning about struct/class mismatch
    
    CaretGeometry is defined as a struct, but was forward-declared as a
    class. Now we forward-declare as a struct. This addresses the
    following Clang warning (that does not appear with GCC):
    
    src/frontends/CaretGeometry.h:27:1: warning: 'CaretGeometry' defined
    as a struct here but previously declared as a class; this is valid,
    but may result in linker errors under the Microsoft C++ ABI
    [-Wmismatched-tags]
---
 src/BufferView.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/src/BufferView.h b/src/BufferView.h
index ca7b20b..1b76da2 100644
--- a/src/BufferView.h
+++ b/src/BufferView.h
@@ -26,7 +26,7 @@ namespace lyx {
 
 namespace support { class FileName; }
 
-namespace frontend { class CaretGeometry; }
+namespace frontend { struct CaretGeometry; }
 namespace frontend { class Painter; }
 namespace frontend { class GuiBufferViewDelegate; }