Take eagerness into account when deduplicating dependencies

[castholm]

Closes #21771

If the same dependency is first discovered as lazy and then later as eager, the existing entry needs to be updated to eager in order for b.dependency() to work.

Tested against the repro in the linked issue. With a master build of Zig it adds an available decl to the generated dependencies.zig, which makes the build system consider it lazy. With this fix the decl is absent and the dependency is correctly considered eager.

diff --git a/.zig-cache/o/0ac409a893112d8a0dadad72e466f606/dependencies.zig b/.zig-cache/o/abff17167087eb0d6564dda2732ee274/dependencies.zig
index 96c1b91..a39ff09 100644
--- a/.zig-cache/o/0ac409a893112d8a0dadad72e466f606/dependencies.zig
+++ b/.zig-cache/o/abff17167087eb0d6564dda2732ee274/dependencies.zig
@@ -1,6 +1,5 @@
 pub const packages = struct {
     pub const @"1220321cdb273d1f6e90b04fc747cae49dac1ae3d7db4125f590d2c0df5c4aadcc88" = struct {
-        pub const available = true;
         pub const build_root = "global_cache\\p\\1220321cdb273d1f6e90b04fc747cae49dac1ae3d7db4125f590d2c0df5c4aadcc88";
         pub const build_zig = @import("1220321cdb273d1f6e90b04fc747cae49dac1ae3d7db4125f590d2c0df5c4aadcc88");
         pub const deps: []const struct { []const u8, []const u8 } = &.{};