The PR had some unforseen perf regressions that are not as easy to find.
Revert the PR for now.
This reverts commit 6ae8912a3e, reversing
changes made to 86d6d2b738.
Backports LLVM commit:
[APFloat] convert SNaN to QNaN in convert() and raise Invalid signal
149f5b573c
SNaN to QNaN conversion also matches what my Intel x86_64 hardware does.