well i tried installing the ppc binary (i assumed it would run ok under rosetta) and it gets a bit further but still with errors:

make compiler_cycle RELEASE=1
make -C compiler cycle
make tempclean ppc3
/bin/rm -f ppcrossppc ppc ppc1 ppc2 ppc3 ./msg2inc
make 'OLDFPC=' next
make rtlclean rtl
make -C /Users/jon/fpc/rtl clean
/bin/rm -f fpcmade.powerpc-darwin Package.fpc ppas.sh script.res link.res
/bin/rm -f *.s *_ppas.sh
make -C darwin clean
/bin/rm -f /Users/jon/fpc/rtl/units/powerpc-darwin/system.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/unixtype.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/ctypes.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/objpas.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/macpas.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/strings.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/sysctl.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/baseunix.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/unixutil.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/unix.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/initc.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/cmem.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/matrix.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/dynlibs.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/dos.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/dl.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/objects.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/printer.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/sockets.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/sysutils.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/typinfo.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/classes.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/math.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/varutils.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/charset.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/ucomplex.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/getopts.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/heaptrc.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/lineinfo.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/errors.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/terminfo.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/termio.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/video.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/crt.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/mouse.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/keyboard.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/console.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/variants.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/types.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/sysctl.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/dateutils.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/sysconst.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/cthreads.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/strutils.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/rtlconsts.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/cwstring.ppu /Users/jon/fpc/rtl/units/powerpc-darwin/fpmkunit.ppu
/bin/rm -f /Users/jon/fpc/rtl/units/powerpc-darwin/math.rst /Users/jon/fpc/rtl/units/powerpc-darwin/varutils.rst /Users/jon/fpc/rtl/units/powerpc-darwin/typinfo.rst /Users/jon/fpc/rtl/units/powerpc-darwin/classes.rst /Users/jon/fpc/rtl/units/powerpc-darwin/variants.rst /Users/jon/fpc/rtl/units/powerpc-darwin/dateutils.rst /Users/jon/fpc/rtl/units/powerpc-darwin/sysconst.rst /Users/jon/fpc/rtl/units/powerpc-darwin/rtlconsts.rst /Users/jon/fpc/rtl/units/powerpc-darwin/fpmkunit.rst
/bin/rm -f fpcmade.powerpc-darwin Package.fpc ppas.sh script.res link.res
/bin/rm -f *.s *_ppas.sh
make -C /Users/jon/fpc/rtl 'OPT=' all
make -C darwin all
/usr/local/bin/ppcppc -dNOMOUSE -Ur -dFPC_USE_LIBC -Ur -Xs -O1r -n -Fi../inc -Fi../powerpc -Fi../unix -Fi../bsd -Fi../bsd/powerpc -Fi../darwin/powerpc -FE. -FU/Users/jon/fpc/rtl/units/powerpc-darwin -dpowerpc -dRELEASE -Us -Sg ../bsd/system.pp
system.pp(257,1) Error: Error while assembling exitcode 1
system.pp(257,1) Fatal: There were 2 errors compiling module, stopping
system.pp(257,1) Fatal: Compilation aborted
and then the terminal is flooded with things like this:

system.pp:39667:no such 386 instruction: `lwz'
system.pp:39668:no such 386 instruction: `li'
system.pp:39669:no such 386 instruction: `addis'
system.pp:39670:more than 1 memory reference in instruction
system.pp:39671:no such 386 instruction: `blt'
system.pp:39672:no such 386 instruction: `li'
system.pp:39673:no such 386 instruction: `addis'
system.pp:39674:invalid character '.' in opcode
system.pp:39675:no such 386 instruction: `beq'
system.pp:39676:invalid character '.' in opcode
system.pp:39677:no such 386 instruction: `beq'
system.pp:39678:invalid character '.' in opcode
system.pp:39679:no such 386 instruction: `bne'
system.pp:39681:no such 386 instruction: `mr'
system.pp:39682:no such 386 instruction: `lwz'
system.pp:39683:no such 386 instruction: `lwz'
system.pp:39684:no such 386 instruction: `lwz'
system.pp:39685:no such 386 instruction: `bl'
system.pp:39686:no such 386 instruction: `mr'
system.pp:39687perands given don't match any known 386 instruction
system.pp:39688:no such 386 instruction: `bge'
system.pp:39689:no such 386 instruction: `lis'