[Bug lto/66180] [6 Regression] many -Wodr false positives when building LLVM with -flto

["hubicka at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66180

--- Comment #4 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
/home/trippels/gcc_6/usr/local/include/c++/6.0.0/bits/stl_pair.h:96:12:
warning: type âstruct pairâ violates one definition rule [-Wodr]
     struct pair
             ^
/home/trippels/gcc_6/usr/local/include/c++/6.0.0/bits/stl_pair.h:96:12: note: a
different type is defined in another translation unit
     struct pair
             ^
/home/trippels/gcc_6/usr/local/include/c++/6.0.0/bits/stl_pair.h:102:11: note:
the first difference of corresponding definitions is field âsecondâ
       _T2 second;                /// @c second is a copy of the second object
            ^
/home/trippels/gcc_6/usr/local/include/c++/6.0.0/bits/stl_pair.h:102:11: note:
a field of same name but different type is defined in another translation unit
       _T2 second;                /// @c second is a copy of the second object
            ^
/home/trippels/llvm/tools/clang/utils/TableGen/ClangDiagnosticsEmitter.cpp:131:10:
note: type âstruct GroupInfoâ defined in anonymous namespace can not match type
âstruct GroupInfoâ
   struct GroupInfo {
           ^
/home/trippels/llvm/tools/clang/utils/TableGen/ClangSACheckersEmitter.cpp:73:8:
note: the incompatible type defined in anonymous namespace in another
translation unit
 struct GroupInfo {
         ^

This looks like a real LLVM bug.  If you do 

class bar {
  anonymous_namespace_type foo; 
}

then definin bar in non-anonymous namespace in more than one unit is ODR
violation (because the type of field FOO is different in each of units).  I
think that it is what the warning is about: the instantiation is non-anonymous
of type _T2=GroupInfo that is anonymous.