fix(linkmodel): key the PE early-out on the target, not the host

The Windows-host if-constexpr broke the linkmodel contract tests on
Windows CI (they resolve synthetic Linux-shaped toolchains anywhere).
Target-keyed is also the semantics a future cross build needs.

Author: Sunrisepeak

src/toolchain/linkmodel.cppm

@@ -228,11 +228,12 @@ ToolchainLinkModel resolve_link_model(const Toolchain& tc) {
     lm.clangDriver  = is_clang(tc);
     lm.clangWithCfg = resolve_clang_driver(tc).hasCfg;
 
-    // Windows / PE: no ELF loader, no rpath, no glibc payload/sysroot model.
+    // PE targets: no ELF loader, no rpath, no glibc payload/sysroot model.
     // MSVC-ABI Clang gets STL+SDK via the driver, MinGW is self-contained —
-    // both want CLibMode::None. Explicit early-out rather than relying on
-    // "no payloads found" falling through to the same answer.
-    if constexpr (mcpp::platform::is_windows) return lm;
+    // both want CLibMode::None. Keyed on the TARGET (not the host) so the
+    // ELF resolution below stays testable anywhere and a future
+    // cross-compile resolves by what it builds FOR.
+    if (is_msvc_target(tc) || is_mingw_target(tc)) return lm;
 
     auto payload_first = [&] {
         auto& pp = *tc.payloadPaths;