Revert "Check new GCC ABI in configure step and eventually fail configuration"

GCC5 ABI patch is in.
This reverts commit 9c2b6c38.

cmake/modules/CheckCompiler.cmake

 #---------------------------------------------------------------------------------------------------
 #  CheckCompiler.cmake
 #---------------------------------------------------------------------------------------------------
-include (CheckCXXSourceCompiles)
 
 #---Enable FORTRAN (unfortunatelly is not not possible in all cases)-------------------------------
 if(fortran)
@@ -53,15 +52,6 @@ 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)