This issue is not specific to Moteino M0. Other M0 boards such as Adafruit Feather M0 also compile incorrectly.
I have been struggling to get my Moteino M0 to work with the MySensors library. After hours of troubleshooting, it seems to be an issue with Platform IO and/or the GNU Arm Embedded Toolchain. I have created issues with Platform IO and the GNU Arm Embedded Toolchain in efforts to resolve issue.
GNU Arm Embedded Toolchain bug: https://bugs.launchpad.net/gcc-arm-embedded/+bug/1836698
Platform IO - Atmelsam platform bug : https://github.com/platformio/platform-atmelsam/issues/70
At this point, I do not know enough to say where the problem is. For now, I would recommend sticking with the trusted Arduino IDE.
Thanks for logging this here, in case others run into something similar, at least they know its a platform bug.
As I found out, the problem is not related to Platform IO. The problem exist in Arduino IDE too. The problem is only related to PRIu8 family of macros and the new format strings introduced in C99. The gcc-arm-embedded toolchain will link with newlib-nano to provide these formatting options. Of course none of us use this expensive formatting functions. :)
References
https://community.arm.com/developer/ip-products/system/b/embedded-blog/posts/shrink-your-mcu-code-size-with-gcc-arm-embedded-4-7
http://www.cplusplus.com/reference/cstdio/printf/