fix: guard POSIX-only unit tests on Windows

- test_toolchain_detect: fake shell script tests skip on Windows
- test_toolchain_registry: expect clang++.exe on Windows
- test_xpkg_emit: sha256_of_file uses sha256sum (Linux only)

Author: Sunrisepeak

tests/unit/test_toolchain_detect.cpp

@@ -54,6 +54,8 @@ esac
 
 } // namespace
 
+#if !defined(_WIN32)
+// Uses a fake shell script as a compiler — POSIX only.
 TEST(ToolchainDetect, ClangVersionOutputIsNotMisclassifiedByGccPaths) {
     auto clang = make_fake_clang();
     TempDirGuard cleanup{clang.parent_path()};
@@ -66,6 +68,7 @@ TEST(ToolchainDetect, ClangVersionOutputIsNotMisclassifiedByGccPaths) {
     EXPECT_EQ(tc->stdlibId, "libc++");
     EXPECT_FALSE(tc->hasImportStd);
 }
+#endif // !defined(_WIN32)
 
 // ─── normalize_driver_output: path-free semantic identity ─────────────
 //
@@ -126,6 +129,7 @@ TEST(NormalizeDriverOutput, EmptyInputProducesEmpty) {
     EXPECT_EQ(normalize_driver_output("\n\n\n"), "");
 }
 
+#if !defined(_WIN32)
 // ─── detect() populates driverIdent ─────────────────────────────────
 TEST(ToolchainDetect, PopulatesDriverIdentFromVersionOutput) {
     auto clang = make_fake_clang();
@@ -138,3 +142,4 @@ TEST(ToolchainDetect, PopulatesDriverIdentFromVersionOutput) {
     EXPECT_NE(tc->driverIdent.find("clang version 20.1.7"), std::string::npos)
         << "driverIdent should contain the --version header: " << tc->driverIdent;
 }
+#endif // !defined(_WIN32)

tests/unit/test_toolchain_registry.cpp

@@ -48,7 +48,11 @@ TEST(ToolchainRegistry, MapsLlvmAndClangAliasesToLlvmPackage) {
     EXPECT_EQ(llvmPkg.display_spec(), "llvm@20.1.7");
     EXPECT_EQ(clangPkg.display_spec(), "clang@20.1.7");
     ASSERT_FALSE(clangPkg.frontendCandidates.empty());
+#if defined(_WIN32)
+    EXPECT_EQ(clangPkg.frontendCandidates.front(), "clang++.exe");
+#else
     EXPECT_EQ(clangPkg.frontendCandidates.front(), "clang++");
+#endif
 }
 
 TEST(ToolchainRegistry, ResolvesPartialMuslVersionForDisplayAndPackage) {

tests/unit/test_xpkg_emit.cpp

@@ -96,6 +96,8 @@ TEST(XpkgEmit, ReleaseTarballUrl) {
     EXPECT_EQ(release_tarball_url("git@github.com:foo/bar.git", "bar", "0.1.0"), "");
 }
 
+#if !defined(_WIN32)
+// sha256_of_file uses sha256sum which is not available on Windows
 TEST(XpkgEmit, Sha256OfFile) {
     using namespace mcpp::publish;
 
@@ -116,6 +118,7 @@ TEST(XpkgEmit, Sha256OfFile) {
     // Non-existent file → empty string
     EXPECT_EQ(sha256_of_file("/no/such/path/zzz"), "");
 }
+#endif // !defined(_WIN32)
 
 TEST(XpkgEmit, LongBracketSequenceInValueIsHarmless) {
     // We emit `"..."` strings, not `[[...]]`, so a literal `]=]` in