[LyX/master] Cmake build: Use the same warning flags at in automake

[Kornel Benko]

commit 4c58315d4b867cf5cce0fa05f168e448381f21d8
Author: Kornel Benko <kornel at lyx.org>
Date:   Thu Nov 26 11:04:48 2020 +0100

    Cmake build: Use the same warning flags at in automake
---
 CMakeLists.txt |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index e2e1e1f..fedcbb1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -706,7 +706,7 @@ else()
 	# The following setting with LYX_GCC11_MODE is needed because cmake does not honor
 	# CMAKE_CXX_STANDARD while performing tests like
 	# check_cxx_source_compiles("..." HAVE_DEF_MAKE_UNIQUE)
-	set(LYX_CXX_FLAGS "-Wall -Wunused-parameter ${LYX_GCC11_MODE}${LYX_CXX_FLAGS}")
+	set(LYX_CXX_FLAGS "-Wall -Wextra -Wno-deprecated-copy ${LYX_GCC11_MODE}${LYX_CXX_FLAGS}")
 	if(LYX_STDLIB_DEBUG)
 	  set(LYX_CXX_FLAGS "${LYX_CXX_FLAGS} -D_GLIBCXX_DEBUG -D_GLIBCXX_DEBUG_PEDANTIC")
         else()