Fix BOOST_NO_CXX11_HDR_UNORDERED_MAP warning

When forcing CXX11 to off, I get the following warning with gcc <4.8:
```
/ssd/deal-git/bundled/boost-1.62.0/include/boost/config/stdlib/libstdcpp3.hpp:182:0: warning: "BOOST_NO_CXX11_HDR_UNORDERED_MAP" redefined
```
This change fixes this.

diff --git a/cmake/configure/configure_boost.cmake b/cmake/configure/configure_boost.cmake
index c96ae66c558d26925be86a8bf0d128ab0fccfb0c..7c8adafb0dd376ed91e8de9c56dcc6117013fb28 100644 (file)
--- a/cmake/configure/configure_boost.cmake
+++ b/cmake/configure/configure_boost.cmake
@@ -38,7 +38,8 @@ MACRO(FEATURE_BOOST_CONFIGURE_COMMON)
   # [1] https://svn.boost.org/trac/boost/ticket/12755
   #
   IF( CMAKE_CXX_COMPILER_ID MATCHES "GNU" AND
-      CMAKE_CXX_COMPILER_VERSION VERSION_LESS "4.8" )
+      CMAKE_CXX_COMPILER_VERSION VERSION_LESS "4.8" AND
+      DEAL_II_WITH_CXX11)
     LIST(APPEND BOOST_DEFINITIONS "BOOST_NO_CXX11_HDR_UNORDERED_MAP")
     LIST(APPEND BOOST_USER_DEFINITIONS "BOOST_NO_CXX11_HDR_UNORDERED_MAP")
   ENDIF()