Implement the first set of changes for PR3963 and rdar://6759604,

which tries to do better error recovery when it is "obvious" that an
identifier is a mis-typed typename.  In this case, we try to parse
it as a typename instead of as the identifier in a declarator, which
gives us several options for better error recovery and immediately
makes diagnostics more useful.  For example, we now produce:

t.c:4:8: error: unknown type name 'foo_t'
static foo_t a = 4;
       ^

instead of:

t.c:4:14: error: invalid token after top level declarator
static foo_t a = 4;
             ^

Also, since we now parse "a" correctly, we make a decl for it,
preventing later uses of 'a' from emitting things like:

t.c:12:20: error: use of undeclared identifier 'a'
int bar() { return a + b; }
                   ^

I'd really appreciate any scrutiny possible on this, it 
is a tricky area.

llvm-svn: 68911