Copy one of amiga_slink.c (assembler=phxass, linker=slink, libraries=SAS)
or amiga_phxlink.c (assembler=phxass, linker=phxlnk, libraries=lcc) to amiga.c.

For floating point stuff, the SAS math libraries don't work. (If we switch to
double instead of extended precision for lcc, scm6881.lib might work.)