1.0.28.15: Build desymlinkification

1.0.28.15: Build desymlinkification

  Changed the object filename computation function to use a different
suffix for files in target-compile mode with the :assem flag.

  Changed the src/compiler/assembly/ paths in build-order.lisp-expr to
refer to src/assembly/ instead.

  Changed the duplicate-stem check in src/cold/shared.lisp to operate
in terms of target-compile object file names.

  Changed both the source and object filename computation functions to
call a new function to remap stem path segments matching "/target/" to
the appropriate per-arch directory.

  Removed the code for creating the compiler/assembly/ and target/
symlinks from make-config.sh.

  With this, source-location information in SBCL is now correct even
when used against an unbuilt source tree.