Fix a backwards compatibility bug found by Tanya. In version 1.2, the

global type plane starts with a length and the TypeTyID value to identify
the type plane has having type definitions. This doesn't happen in 1.3
because the types are read from a known position in the file. However, the
TypeTyID must be read in (and ignored) if its a 1.2 bytecode file.

llvm-svn: 14728