multimc: fix build with Qt 5.11, fix desktop icon

[kliu128]

Motivation for this change

MultiMC build has been broken since the upgrade to Qt 5.11 (see #42387). As mentioned in that issue, the desktop icon is also broken.

MultiMC had a patch upstream to fix build with Qt 5.11, but it hasn't hit a stable release yet, and applying the patch on top of 0.6.2 fails (see, again, discussion in #42387).

Things done

• Updated MultiMC temporarily to the latest commit from MultiMC's develop branch, where the Qt 5.11 fix has been applied.
• Created a compatibility symlink from MultiMC → multimc to fix the desktop icon.

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Fits CONTRIBUTING.md.

---

[xeji]

@GrahamcOfBorg build multimc

[GrahamcOfBorg]

No attempt on x86_64-darwin (full log)

The following builds were skipped because they don't evaluate on x86_64-darwin: multimc

Partial log (click to expand)

a) For `nixos-rebuild` you can set
  { nixpkgs.config.allowUnsupportedSystem = true; }
in configuration.nix to override this.

b) For `nix-env`, `nix-build`, `nix-shell` or any other Nix command you can add
  { allowUnsupportedSystem = true; }
to ~/.config/nixpkgs/config.nix.

[GrahamcOfBorg]

No attempt on aarch64-linux (full log)

The following builds were skipped because they don't evaluate on aarch64-linux: multimc

Partial log (click to expand)

a) For `nixos-rebuild` you can set
  { nixpkgs.config.allowUnfree = true; }
in configuration.nix to override this.

b) For `nix-env`, `nix-build`, `nix-shell` or any other Nix command you can add
  { allowUnfree = true; }
to ~/.config/nixpkgs/config.nix.

[GrahamcOfBorg]

Failure on x86_64-linux (full log)

Attempted: multimc

Partial log (click to expand)

Resolving deltas: 100% (292/292), done.
From https://github.com/MultiMC/MultiMC5
 * branch            HEAD       -> FETCH_HEAD
Switched to a new branch 'fetchgit'
Submodule 'depends/libnbtplusplus' (https://github.com/MultiMC/libnbtplusplus.git) registered for path 'libraries/libnbtplusplus'
Submodule 'libraries/quazip' (https://github.com/MultiMC/quazip.git) registered for path 'libraries/quazip'
error: key does not contain a section: .url
builder for '/nix/store/k2fx5w7a8ix6raxmmpkf2ikrb5zzv482-source.drv' failed with exit code 1
cannot build derivation '/nix/store/plnjfrbaib63bwi2sdvp6gma2kf1f5sb-multimc-unstable-2018-06-04.drv': 1 dependencies couldn't be built
error: build of '/nix/store/plnjfrbaib63bwi2sdvp6gma2kf1f5sb-multimc-unstable-2018-06-04.drv' failed

[xeji]

@GrahamcOfBorg build multimc

[GrahamcOfBorg]

No attempt on x86_64-darwin (full log)

The following builds were skipped because they don't evaluate on x86_64-darwin: multimc

Partial log (click to expand)

a) For `nixos-rebuild` you can set
  { nixpkgs.config.allowUnsupportedSystem = true; }
in configuration.nix to override this.

b) For `nix-env`, `nix-build`, `nix-shell` or any other Nix command you can add
  { allowUnsupportedSystem = true; }
to ~/.config/nixpkgs/config.nix.

[GrahamcOfBorg]

No attempt on aarch64-linux (full log)

The following builds were skipped because they don't evaluate on aarch64-linux: multimc

Partial log (click to expand)

a) For `nixos-rebuild` you can set
  { nixpkgs.config.allowUnfree = true; }
in configuration.nix to override this.

b) For `nix-env`, `nix-build`, `nix-shell` or any other Nix command you can add
  { allowUnfree = true; }
to ~/.config/nixpkgs/config.nix.

[GrahamcOfBorg]

Success on x86_64-linux (full log)

Attempted: multimc

Partial log (click to expand)

shrinking /nix/store/6f6d1v2mlm60la4fx8nmlqh27svpdmcp-multimc-unstable-2018-06-04/bin/libMultiMC_logic.so
shrinking /nix/store/6f6d1v2mlm60la4fx8nmlqh27svpdmcp-multimc-unstable-2018-06-04/bin/.MultiMC-wrapped
shrinking /nix/store/6f6d1v2mlm60la4fx8nmlqh27svpdmcp-multimc-unstable-2018-06-04/bin/libMultiMC_gui.so
strip is /nix/store/4qvrxzxa535y8304mk195x50b6p9607d-binutils-2.30/bin/strip
stripping (with command strip and flags -S) in /nix/store/6f6d1v2mlm60la4fx8nmlqh27svpdmcp-multimc-unstable-2018-06-04/bin
patching script interpreter paths in /nix/store/6f6d1v2mlm60la4fx8nmlqh27svpdmcp-multimc-unstable-2018-06-04
/nix/store/6f6d1v2mlm60la4fx8nmlqh27svpdmcp-multimc-unstable-2018-06-04/MultiMC: interpreter directive changed from "/bin/bash" to "/nix/store/8zkg9ac4s4alzyf4a8kfrig1j73z66dw-bash-4.4-p23/bin/bash"
checking for references to /build in /nix/store/6f6d1v2mlm60la4fx8nmlqh27svpdmcp-multimc-unstable-2018-06-04...
postPatchMkspecs
/nix/store/6f6d1v2mlm60la4fx8nmlqh27svpdmcp-multimc-unstable-2018-06-04