* wait, adding mthumb might have changed things, now I have
```
/usr/lib/gcc/arm-none-eabi/12.2.1/../../../arm-none-eabi/bin/ld: /build/newlib-pB30de/newlib-3.3.0/build/arm-none-eabi/thumb/v7e-m+fp/hard/newlib/libc/stdlib/../../../../../../../../newlib/libc/stdlib/dtoa.c:352: undefined reference to `__aeabi_dsub'
```