diff -rupN {old,root-*}/cmake/modules/CheckCompiler.cmake
--- old/cmake/modules/CheckCompiler.cmake	2016-07-06 18:36:49.000000000 +0200
+++ root-6.06.06/cmake/modules/CheckCompiler.cmake	2016-08-05 14:28:00.218968142 +0200
@@ -51,15 +51,6 @@ if (CMAKE_COMPILER_IS_GNUCXX)
   endif()
   message(STATUS "Found GCC. Major version ${GCC_MAJOR}, minor version ${GCC_MINOR}")
   set(COMPILER_VERSION gcc${GCC_MAJOR}${GCC_MINOR}${GCC_PATCH})
-  CHECK_CXX_SOURCE_COMPILES("
-    #include <string>
-    #if _GLIBCXX_USE_CXX11_ABI
-    #error \"cling does not support GCC 5 ABI.\"
-    #endif
-    int main() {}" CXX_SUPPORTS_OLD_ABI)
-  if(NOT CXX_SUPPORTS_OLD_ABI)
-     message(FATAL_ERROR "Found GCC compiler with new ABI. Cling does not support the GCC 5 ABI yet")
-  endif()
 else()
   set(GCC_MAJOR 0)
   set(GCC_MINOR 0)