Make the guard for external ABI libraries include the guard for
libsupc++ in typeinfo.cpp, bringing it into agreement with
exception.cpp. This fixes link errors due to duplicate symbols from
this translation unit.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@191397 91177308-0d34-0410-b5e6-96231b3b80d8