The PR had some unforseen perf regressions that are not as easy to find.
Revert the PR for now.
This reverts commit 6ae8912a3e7d2c4c775024f58a7ba4b1aedc4073, reversing
changes made to 86d6d2b7389fe1b339402c1798edae8b695fc9ef.
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.