This patch mechanically replaces None with std::nullopt where the
compiler would warn if None were deprecated. The intent is to reduce
the amount of manual work required in migrating from Optional to
std::optional.
This is part of an effort to migrate from llvm::Optional to
std::optional:
https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716
fixed fields with highly-aligned flexible fields.
The code was not considering the possibility that aligning
the current offset to the alignment of a queue might push
us past the end of the gap. Subtracting the offsets to
figure out the maximum field size for the gap then overflowed,
making us think that we had nearly unbounded space to fill.
Fixes PR 51131.
