flake.lock: Update to latest nixpkgs

This is to make sure we test against the latest set of GCC and LLVM
compilers, since we haven't updated them for a while.

Flake lock file updates:

• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/e0e6b6909977de63dab514efbf5470bc31e7055e?narHash=sha256-YiFBn3K4l1AzVt8NeSg9ZJNvHxX2k%2BAkS74s/s4ASRA%3D' (2023-08-01)
  → 'github:NixOS/nixpkgs/4284c2b73c8bce4b46a6adf23e16d9e2ec8da4bb?narHash=sha256-i4vJL12/AdyuQuviMMd1Hk2tsGt02hDNhA0Zj1m16N8%3D' (2024-07-05)

Signed-off-by: aszlig <aszlig@nix.build>

flake.nix

@@ -27,7 +27,7 @@
 
       mesonFlags = [ "-Dtest-timeout=3600" ] ++ attrs.mesonFlags or [];
 
-      nativeBuildInputs = [ pkgs.meson pkgs.ninja pkgs.pkgconfig ]
+      nativeBuildInputs = [ pkgs.meson pkgs.ninja pkgs.pkg-config ]
                        ++ attrs.nativeBuildInputs or [];
       buildInputs = [ libyamlcpp ] ++ attrs.buildInputs or [];
 
@@ -314,7 +314,16 @@
         in lib.optional (majorVersion != null && isEligible) {
           name = "${compiler}${lib.head majorVersion}";
           value = lib.genAttrs req.systems (withSystemFull getPackageAttrs);
-        }) nixpkgs.legacyPackages.x86_64-linux;
+        }) (import nixpkgs {
+          # We use x86_64-linux only for evaluating the package attributes
+          # available, the final evaluation of the packages themselves are done
+          # using the real target system.
+          system = "x86_64-linux";
+          # This is to avoid evaluation errors. For example llvmPackages_10 has
+          # been removed and with aliases enabled, we get an attribute that
+          # directly leads to a "throw".
+          config.allowAliases = false;
+        });
 
       in lib.listToAttrs (mapAttrsToOneList mkCompilerPackages {
         clang = {