Upgrade to LLVM 18 and fix nix shell

[alfreb]

Depends on #2246 and can only be merged after that.

• Upgrades IncludeOS to build with LLVM 18. This will unlock most C++20 features in libc++
• Fixes the nix shell to use the IncludeOS package, building with cmake in a tempdir or a build path passed in via --argstr.

Build tested with

export INCLUDEOS_CHAINLOADER=$(nix-build chainloader.nix)/bin \
            && nix-build example.nix  \
            && boot ./result/bin/hello_includeos.elf.bin

It successfully builds and boots the example.

Shell tested with nix-shell and nix-shell --argstr build_example. It successfully builds the example and enters the nix shell in a working cmake build dir.

[alfreb]

The last commit adds a unikernel parameter, allowing the same nix shell to build any unikernel. Tested with nix-shell --argstr unikernel ./example which succeeds, and nix-shell --argstr unikernel ./test/net/integration/udp/ which correctly fails as that test is broken and needs fixing.

[MagnusS]

Nice! I've merged #2246, this may need a rebase

[alfreb]

Rebased now

[alfreb]

Great! Now it looks like all we need to do is remove the conan stuff from cmake and some of these tests will build cleanly! I made the change for the UDP test as an example. I haven't run the test, but it boots!

SeaBIOS (version 1.16.3-debian-1.16.3-2)
Booting from ROM..* Multiboot begin: 0x9500
* Multiboot cmdline @ 0x234023: /nix/store/dcbw0cibwmfrlv8r79az05i7h1cygraf-chainloader-static-i686-unknown-linux-musl-dev/bin/chainloader ""
* Multiboot end: 0x234091
* Module list @ 0x234000
     * Module @ 0x235000
     * Args: net_udp.elf.bin ""
     * End: 0x47dac0
 * Multiboot end: 0x47dac0
<Multiboot>Booted with multiboot
    * Boot flags: 0x24f
    * Valid memory (409087 Kib):
      0x00000000 - 0x0009fbff (639 Kib)
      0x00100000 - 0x18fdffff (408448 Kib)

    * Booted with parameters @ 0x234023: /nix/store/dcbw0cibwmfrlv8r79az05i7h1cygraf-chainloader-static-i686-unknown-linux-musl-dev/bin/chainloader ""
    * Multiboot provided memory map  (8 entries @ 0x9000)
      0x0000000000 - 0x000009fbff FREE (639 Kb.)
      0x000009fc00 - 0x000009ffff RESERVED (1 Kb.)
      0x00000f0000 - 0x00000fffff RESERVED (64 Kb.)
      0x0000100000 - 0x0018fdffff FREE (408448 Kb.)
      0x0018fe0000 - 0x0018ffffff RESERVED (128 Kb.)
      0x00feffc000 - 0x00feffffff RESERVED (16 Kb.)
      0x00fffc0000 - 0x00ffffffff RESERVED (256 Kb.)
      0x0000000000 - 0x00ffffffff RESERVED (0 Kb.)

<Multiboot>OS loaded with 1 modules
    * net_udp.elf.bin "" @ 0x235000 - 0x47dac0, size: 2394816b
* Multiboot begin: 0x9500
* Multiboot end: 0x3a6468
[x86_64 PC] constructor
[ Machine ] Initializing heap
[ Machine ] Main memory detected as 415469376 b
[ Machine ] Reserving 1048576 b for machine use
<Multiboot>Booted with multiboot
    * Boot flags: 0x24f
    * Valid memory (409087 Kib):
      0x00000000 - 0x0009fbff (639 Kib)
      0x00100000 - 0x18fdffff (408448 Kib)

    * Booted with parameters @ 0x8000: net_udp.elf.bin ""
    * Multiboot provided memory map  (8 entries @ 0x9000)
      0x0000000000 - 0x000009fbff FREE (639 Kb.)
      0x000009fc00 - 0x000009ffff RESERVED (1 Kb.)
      0x00000f0000 - 0x00000fffff RESERVED (64 Kb.)
      0x0000100000 - 0x0018fdffff FREE (408448 Kb.)
      0x0018fe0000 - 0x0018ffffff RESERVED (128 Kb.)
      0x00feffc000 - 0x00feffffff RESERVED (16 Kb.)
      0x00fffc0000 - 0x00ffffffff RESERVED (256 Kb.)
      0xfd00000000 - 0xffffffffff RESERVED (12582912 Kb.)
================================================================================
 IncludeOS VERY_DIRTY (x86_64 / 64-bit)
 +--> Running [ UDP test ]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    [ Network ] Creating stack for VirtioNet on eth0 (MTU=1500)
       [ Inet ] Bringing up eth0 on CPU 0
       [ Inet ] Network configured (c0:01:0a:00:00:2a)
                IP:         10.0.0.55
                Netmask:    255.255.0.0
                Gateway:    10.0.0.1
                DNS Server:     10.0.0.1
      [ Inet6 ] Address configured fe80:0:0:0:0:0:0:4242/64
[ UDP test service ] Listening on port 4242