The short version is newlib gets built with support only for a default
-mhwmult=16 which causes the MCU to reset when invoking strtoul in an
application targeting -mhwmult=f5series, because there is no MPY peripheral
at the addresses where the operands are written. mhwmult needs to be one
of the features that distinguish multilib selection.
It'd also probably be better to make the default in msp430_output_labelref
select msp430_no_hwmult which will (at least theoretically) work on every