[codeview] Truncate records to maximum record size near 64KB

If we don't truncate, LLVM asserts when the label difference doesn't fit
in a 16 bit field. This patch truncates two kinds of data: trailing null
terminated names in symbol records, and inline line tables. The inline
line table test that I have is too large (many MB), so I'm not checking
it in.

Hopefully fixes PR28264.

llvm-svn: 283403