record accurate sourceloc info for storage class specs, so we can report

things like:

t.c:4:10: error: invalid storage class specifier in function declarator
int foo2(auto int Aaslfkasdflkj, register B);
         ^

instead of:

t.c:4:19: error: invalid storage class specifier in function declarator
int foo2(auto int Aaslfkasdflkj, register B);
                  ^

llvm-svn: 39224