Make the implicit-int handling error recovery stuff handle C++

nested name specifiers.  Now we emit stuff like:

t.cpp:8:13: error: unknown type name 'X'
static foo::X  P;
       ~~~~ ^

instead of:

t.cpp:8:16: error: invalid token after top level declarator
static foo::X  P;
               ^

This is inspired by a really awful error message I got from 
g++ when I misspelt diag::kind as diag::Kind.

llvm-svn: 69086