Also weaken `__floattidf`

Fixes link error with ion shell.

With a fresh bootstrap of the redox source, I encountered a link error with the ion shell. See snippet for details:

https://gitlab.redox-os.org/snippets/1316

@4lDO2 suggested the fix:

https://chat.redox-os.org/redox/pl/tdx8rfdgy3gczeyy19dbpzhara

It seems there are more symbols that need to be added, based on recent discussion in #general.

merged

mentioned in commit 91f0be87