This issue was discussed at #106795
and at #106796 (comment)

Some functions in core::sync are defined to only compile if the target has 8-bit atomic support. While they should be compiled for all targets with atomic support.

This can cause unnecessary compilation issues when using a custom target json.

This can probably be solved by changing the definitions to

#[cfg(any(
    target_has_atomic = "8",
    target_has_atomic = "16",
    target_has_atomic = "32",
    target_has_atomic = "64",
    target_has_atomic = "128",
    target_has_atomic = "ptr"
))]

from

#[cfg(target_has_atomic = "8")]

like you can see at vadorovsky@041978b

Examples:

@vadorovsky @alessandrod