fix(ci: build): manually build instead of nix build

This should be temporary, until we find a way to download git submodules
(criterion) inside the nix derivation since it breaks meson currently
(and that I really don't want to deal with meson nor nix rn).

.github/workflows/build.yml

@@ -28,4 +28,8 @@ jobs:
 
     - name: Build Kernel
       run: |
-        nix build .#kernel -L
+        nix develop --command ninja -C build kernel
+
+    - name: Build ISO
+      run: |
+        nix develop --command ninja -C build iso

flake.nix

@@ -63,6 +63,11 @@
 
               buildInputs = [ pkgs.pkgsi686Linux.glibc ];
               hardeningDisable = [ "fortify" ];
+
+              shellHook = ''
+                export BUILD_DIR=build
+                meson setup --cross-file ./scripts/meson_cross.ini --reconfigure -Dbuildtype=debug "./$BUILD_DIR"
+              '';
             };
 
             test = pkgs.mkShell rec {

meson.build

@@ -70,7 +70,7 @@ run_target('qemu',
 
 if get_option('buildtype') == 'debug'
 
-gdb = find_program('gdb')
+gdb = find_program('gdb', false)
 
 # We need to use a custom target to be able to daemonize appropriately
 custom_target('qemu-server',