The Z80 assembler does not support the defm directive; defm is equivalent to the defb/db directives, and is often used to define pure text strings as opposed to numeric byte values. Support for the defm directive would be a nice addition for compatibility with other Z80 assemblers.
Please close as fixed: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=6655dba246bd164d953fe220a0e3d4eed85bb268
Fixed