test: a project and its pragma dependency load a shared sibling apart

The fixture app has `#pragma crafter dependency "../tool"` and loads
../shared for itself, which the tool loads too; the app is loaded with
no args, the case where the two cache keys used to match. With
CRAFTER_BUILD_MARCH=x86-64-v2, the app's copy of shared has to keep
that march and no -fPIC, and the tool's copy has to be host tooling.
Before the fix the app got the tool's copy back: one Configuration,
with march native and -fPIC.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/HostToolingSibling/fixture/shared/project.cpp

@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: LGPL-3.0-only
+// SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®
+
+import std;
+import Crafter.Build;
+namespace fs = std::filesystem;
+using namespace Crafter;
+
+// The sibling both the tool and the app load. ApplyStandardArgs on purpose:
+// it reads CRAFTER_BUILD_MARCH from the environment, which is how the test
+// tells the app's copy from the one built as host tooling.
+extern "C" Configuration CrafterBuildProject(std::span<const std::string_view> args) {
+    Configuration cfg;
+    cfg.path = "./";
+    cfg.name = "shared";
+    cfg.outputName = "shared";
+    cfg.type = ConfigurationType::LibraryStatic;
+    ApplyStandardArgs(cfg, args);
+    std::array<fs::path, 1> ifaces = { "interfaces/Shared" };
+    std::array<fs::path, 0> impls = {};
+    cfg.GetInterfacesAndImplementations(ifaces, impls);
+    return cfg;
+}