[LyX/master] Cmake build: Remove unnecessary duplication of c++ flags

[Kornel Benko]

commit 0f881e202eb0514a569d5d1ddc5584d577124151
Author: Kornel Benko <kor...@lyx.org>
Date:   Thu Jul 27 13:33:17 2017 +0200

    Cmake build: Remove unnecessary duplication of c++ flags
    
    Apparently cmake concatenates CMAKE_CXX_FLAGS to the Release and Debug flags
    Also eliminated the mix of '-std=c++*' and '-std=gnu++*' flags
---
 CMakeLists.txt |   10 +++++++---
 1 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7490545..6975751 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -8,6 +8,10 @@ cmake_minimum_required(VERSION 2.6.4)
 
 set(LYX_PROJECT LyX)
 
+# Instruct cmake to not use gnu extensions,
+# this prevents the mix of '-std=c++*' and '-std=gnu++*' flags
+set(CMAKE_CXX_EXTENSIONS OFF)
+
 enable_testing()
 
 get_filename_component(lyx_dir_readme ${CMAKE_SOURCE_DIR}/README REALPATH) # 
Resolve symlinks
@@ -593,11 +597,11 @@ if(NOT MSVC)
                set(LYX_CXX_FLAGS "${LYX_CXX_FLAGS} -D_GLIBCXX_DEBUG 
-D_GLIBCXX_DEBUG_PEDANTIC")
        endif()
        set(CMAKE_CXX_FLAGS       "${LYX_CXX_FLAGS} -fno-strict-aliasing " 
CACHE TYPE STRING FORCE)
-       set(CMAKE_CXX_FLAGS_DEBUG "${LYX_CXX_FLAGS} -fno-strict-aliasing -O0 
-g3 -D_DEBUG" CACHE TYPE STRING FORCE)
+       set(CMAKE_CXX_FLAGS_DEBUG "-O0 -g3 -D_DEBUG" CACHE TYPE STRING FORCE)
        if(MINGW)
-               set(CMAKE_CXX_FLAGS_RELEASE "${LYX_CXX_FLAGS} -O2 -DNDEBUG" 
CACHE TYPE STRING FORCE)
+               set(CMAKE_CXX_FLAGS_RELEASE "-O2 -DNDEBUG" CACHE TYPE STRING 
FORCE)
        else()
-               set(CMAKE_CXX_FLAGS_RELEASE "${LYX_CXX_FLAGS} -O3 -DNDEBUG" 
CACHE TYPE STRING FORCE)
+               set(CMAKE_CXX_FLAGS_RELEASE "-O3 -DNDEBUG" CACHE TYPE STRING 
FORCE)
        endif()
 endif()