[codeview] Add support for new type records.

This adds support for parsing and dumping the following
symbol types:

S_LPROCREF
S_ENVBLOCK
S_COMPILE2
S_REGISTER
S_COFFGROUP
S_SECTION
S_THUNK32
S_TRAMPOLINE

As of this patch, the test PDB files no longer have any unknown
symbol types.

llvm-svn: 270628