lang/rust: Cleanup armv6 / armv7 workarounds

[mikael]

Summary

This issues is solved with the new bootstraps (on armv6 and armv7):
PR: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=256135

ld.bfd is not present on 11.4, so we can remove the cc-wrapper:
https://reviews.freebsd.org/D23385#513496

We can remove the cc-wrapper for armv6 when 11.4 goes EOL:

To be merged with the rust 1.56 update.

[tobik]

LGTM.

Do we need to keep this after @rene commits D32008? If not we could remove it earlier than 1.56.

[mikael]

In D32157#725775, @tobik wrote:

LGTM.

Do we need to keep this after @rene commits D32008? If not we could remove it earlier than 1.56.

Better commit that with rust 1.56, it doesn't fix important things.