makelib.gen: Added -ffat-lto-objects to library compile options. Without this, newer linkers strip vital symbols which cause the final link to fail.
makefile.gen: Added -flto to final link stage. Also added -m68000 as some newer linkers generate non-68k code without this which cause runtime exceptions.
common.mk: Changed PREFIX setting from := to ?= so it can be overridden from an environment variable.
Fixed compiler warnings in string.c. Double use of const.
Changes have been confirmed to work in the default Windows environment.
Changes have been confirmed to work in the default Windows environment.