Cmake flags update (#1539)

* Added cmake flags to specify D_GLIBCXX_USE_CXX11_ABI and disable building of doc

* Renamed the NGRAPH_DOC_BUILD_ENABLE flag based on PR feedback

CMakeLists.txt

@@ -140,6 +140,13 @@ endif()
 
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
 
+if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
+    if (DEFINED NGRAPH_USE_CXX_ABI)
+        message( STATUS "nGraph using CXX11 ABI: " ${NGRAPH_USE_CXX_ABI} )
+        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -D_GLIBCXX_USE_CXX11_ABI=${NGRAPH_USE_CXX_ABI}")
+    endif()    
+endif()
+
 ngraph_var(NGRAPH_WARNINGS_AS_ERRORS DEFAULT "OFF")
 if (${NGRAPH_WARNINGS_AS_ERRORS})
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror")
@@ -281,4 +288,7 @@ else()
     message(STATUS "unit tests disabled")
 endif()
 
-add_subdirectory(doc)
+if (NGRAPH_DOC_BUILD_ENABLE)
+    add_subdirectory(doc)
+endif()
+