use current-compile-output-dir for intermediate compilation objects

[corpix]

This patch force Gerbil (and Gambit) to write intermediate compilation objects into (current-compile-output-dir). Motivated by this error:

Some more context could be found on Gerbil support channel here.

$ gxc -static -exe -o app app.ss                                                                   
/nix/store/i2fr4hsl5bs704bp8kihxdxbnvcsm3h3-gerbil-cli/gerbil/lib/static/cli__cli.scm:
*** ERROR IN c#targ-start-dump -- Read-only file system
(open-output-file "/nix/store/i2fr4hsl5bs704bp8kihxdxbnvcsm3h3-gerbil-cli/gerbil/lib/static/cli__cli.c")
#f*** ERROR IN gxc#compile-executable-module/separate -- 
*** ERROR IN ?
--- Syntax Error at (compile-exe app.ss): Compilation error; process exit with nonzero status
... form:   ("/nix/store/58g7klswv88zp6d3kmdzyk67rf3x5035-gerbil-gerbil-unstable-2024-05-11/gerbil/v0.18.1/bin/gsc"
             "-link"
             "/nix/store/58g7klswv88zp6d3kmdzyk67rf3x5035-gerbil-gerbil-unstable-2024-05-11/gerbil/v0.18.1/lib/static/gerbil__runtime__gambit.c"
             ...
$ echo $GERBIL_LOADPATH
/nix/store/i2fr4hsl5bs704bp8kihxdxbnvcsm3h3-gerbil-cli/gerbil/lib

Quick demonstration of the effect this patch has on gxc:

 ~/projects/src/github.com/mighty-gerbils/gerbil  λ  ls -la ~/.gerbil                                                 ✖ 2
"/home/user/.gerbil": No such file or directory (os error 2)
 ~/projects/src/github.com/mighty-gerbils/gerbil  λ  cat hello.ss
(export main)
(def (main . args)
     (displayln "hello"))

 ~/projects/src/github.com/mighty-gerbils/gerbil  λ  gxc -exe -static hello.ss                                        (5s 732ms)
/home/user/.gerbil/lib/static/schemered__hello.scm:
/home/user/.gerbil/lib/hello__exe.scm:
...

 ~/projects/src/github.com/mighty-gerbils/gerbil  λ  ./hello                                                          (1s 739ms)
hello
 ~/projects/src/github.com/mighty-gerbils/gerbil  λ  tree ~/.gerbil/lib
/home/user/.gerbil/lib
├── hello__exe.scm
├── schemered
│   ├── hello~0.scm
│   ├── hello.scm
│   └── hello.ssi
└── static
    ├── schemered__hello.c
    ├── schemered__hello.o
    └── schemered__hello.scm

3 directories, 7 files
 ~/projects/src/github.com/mighty-gerbils/gerbil  λ  ls -la hello*
.rwxr-xr-x 15M user 20 Jul 00:57 hello
.rw-r--r--  59 user 20 Jul 00:57 hello.ss

This patch depends on changes in Gambit (but I am not sure, maybe we could improve it, so we don't need to change any thing in Gambit?) gambit/gambit#914

[netlify]

👷 Deploy request for elastic-ritchie-8f47f9 pending review.

Visit the deploys page to approve it

Name	Link
🔨 Latest commit	8acf2d6

[vyzo]

This is going to break hermetic package builds and mix/bleed intermediate build artifacts in a shared ditectory.

So this is not the right thing to do in the general case and it cannot be the default behavior.

We should only enable this when needed (eg for problem systems like nix), either with an env var or pethaps with a separate option?
Either way something the user says.

[fare]

The real fix is that the nix packaging needs to be updated to include pre-compiled objects.