Fails to compile on target thumbv6m-none-eabi

[machado2]

cargo build --release --target thumbv6m-none-eabi
Compiling cty v0.2.1
Compiling memchr v2.3.3
Compiling cstr_core v0.2.2
error[E0432]: unresolved import alloc::sync
--> C:*****.cargo\registry\src\github.com-1ecc6299db9ec823\cstr_core-0.2.2\src\lib.rs:21:12
|
21 | use alloc::sync::Arc;
| ^^^^ could not find sync in alloc

error: aborting due to previous error

[Amanieu]

You'll want to disable the arc feature on that target.