[modules] Write the options records to a separate subblock rather than writing

[modules] Write the options records to a separate subblock rather than writing
them directly to the control block. These are fairly large, and in a build with
lots of modules / chained PCH, we don't need to read most of them. No
functionality change intended.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@247055 91177308-0d34-0410-b5e6-96231b3b80d8