[clang-doc] Bump BitcodeWriter max line number to 32U

PR43039 reports hitting the assert on a very large file, so bumping this
to allow for larger files.

Differential Revision: https://reviews.llvm.org/D66681

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@369811 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed