[LyX/master] CMake: allow compile-time C++ flags to be set

[Scott Kostyshak]

commit 374cf6a39f321c7843b36aab242e0852b01887b8
Author: Scott Kostyshak <skost...@lyx.org>
Date:   Fri Nov 29 21:08:48 2013 -0500

    CMake: allow compile-time C++ flags to be set
    
    For example, one could run CMake as follows:
      cmake -DLYX_CXX_FLAGS_EXTRA="-Werror"
    
    Thanks to Kornel.

diff --git a/CMakeLists.txt b/CMakeLists.txt
index c285dc0..c0fd673 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -468,6 +468,10 @@ if(NOT MSVC)
        endif()
 endif()
 
+if(LYX_CXX_FLAGS_EXTRA)
+       add_definitions(${LYX_CXX_FLAGS_EXTRA})
+endif()
+
 find_package(Qt5Core QUIET)
 if (Qt5Core_FOUND)
        find_package(Qt5Widgets REQUIRED)