ctfconvert: Demote lack of DWARF to a warning

[emaste]

Summary

Assembly files may not have DWARF info.

[markj]

Which file triggered this problem?

[emaste]

@des shared https://ci.freebsd.org/job/FreeBSD-main-amd64-gcc14_build/5142/console

02:57:24 --- exception.o ---
02:57:24 /workspace/src/sys/amd64/amd64/exception.S: Assembler messages:
02:57:24 /workspace/src/sys/amd64/amd64/exception.S:617: Warning: no instruction mne=
02:57:24 monic suffix given and no register operands; using default for `sysret'
02:57:24 ctfconvert -L VERSION -g exception.o
02:57:24 ERROR: ctfconvert: file does not contain dwarf type data (try compiling wit=
02:57:24 h -g)
02:57:24 *** [exception.o] Error code 1
02:57:24 
02:57:24 make[2]: stopped making "all" in /tmp/obj/workspace/src/amd64.amd64/sys/GEN=
02:57:24 ERIC