fix: address code review feedback for Windows support

- Default toolchain on Windows falls back to llvm@20.1.7 (was musl-gcc)
- probe_compiler_binary: take first line from `where` output (multi-line)
- Library output naming: .lib/.dll on Windows (was .a/.so)

Author: Sunrisepeak

src/build/plan.cppm

@@ -172,10 +172,18 @@ BuildPlan make_plan(const mcpp::manifest::Manifest&         manifest,
         lu.targetName = t.name;
         if (t.kind == mcpp::manifest::Target::Library) {
             lu.kind   = LinkUnit::StaticLibrary;
+#if defined(_WIN32)
+            lu.output = std::filesystem::path("bin") / std::format("{}.lib", t.name);
+#else
             lu.output = std::filesystem::path("bin") / std::format("lib{}.a", t.name);
+#endif
         } else if (t.kind == mcpp::manifest::Target::SharedLibrary) {
             lu.kind   = LinkUnit::SharedLibrary;
+#if defined(_WIN32)
+            lu.output = std::filesystem::path("bin") / std::format("{}.dll", t.name);
+#else
             lu.output = std::filesystem::path("bin") / std::format("lib{}.so", t.name);
+#endif
         } else if (t.kind == mcpp::manifest::Target::TestBinary) {
             lu.kind   = LinkUnit::TestBinary;
 #if defined(_WIN32)

src/cli.cppm

@@ -1135,15 +1135,15 @@ prepare_build(bool print_fingerprint,
         // macOS: LLVM/Clang — Apple doesn't ship GCC; upstream LLVM with
         //        bundled libc++ is the self-contained choice.
         // Linux: musl-gcc — produces portable static binaries.
-#if defined(__APPLE__)
+#if defined(__APPLE__) || defined(_WIN32)
         std::string defaultSpec = "llvm@20.1.7";
 #else
         std::string defaultSpec = "gcc@15.1.0-musl";
 #endif
         auto defaultParsed = mcpp::toolchain::parse_toolchain_spec(defaultSpec);
         auto defaultPkg = mcpp::toolchain::to_xim_package(*defaultParsed);
 
-#if defined(__APPLE__)
+#if defined(__APPLE__) || defined(_WIN32)
         mcpp::ui::info("First run",
             std::format("no toolchain configured — installing {} (LLVM/Clang) as default",
                         defaultSpec));

src/toolchain/probe.cppm

@@ -257,7 +257,8 @@ probe_compiler_binary(const std::filesystem::path& explicit_compiler) {
     if (!bin_path_r) {
         return std::unexpected(DetectError{std::format("compiler '{}' not found in PATH", cxx)});
     }
-    auto bin = trim_line(*bin_path_r);
+    // `where` on Windows may return multiple lines; take only the first.
+    auto bin = trim_line(first_line_of(*bin_path_r));
     if (bin.empty()) {
         return std::unexpected(DetectError{std::format("compiler '{}' not found", cxx)});
     }