[LyX/master] Cmake build: Abort build-configuration if using a too old c++ gnu compiler

[Kornel Benko]

commit e3524cefaa9bc6ebe1b9f0d31ad627dbb8bfb9d8
Author: Kornel Benko <kor...@lyx.org>
Date:   Thu May 14 21:21:07 2015 +0200

    Cmake build: Abort build-configuration if using a too old c++ gnu compiler

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 785e37e..5315326 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -68,8 +68,15 @@ if(LYX_XMINGW)
 endif()
 
 if(NOT help AND NOT HELP)
-       # 'project' triggers the searching for a compiler
-       project(${LYX_PROJECT})
+  # 'project' triggers the searching for a compiler
+  project(${LYX_PROJECT})
+  if (CMAKE_COMPILER_IS_GNUCXX)
+    if (CMAKE_CXX_COMPILER_VERSION VERSION_LESS "4.0")
+      message(STATUS "Gnu CXX compiler version = 
${CMAKE_CXX_COMPILER_VERSION}")
+      message(STATUS "is too old, should be >= 4.0")
+      message(FATAL_ERROR "Exiting")
+    endif()
+  endif()
 endif()
 
 if(UNIX)