build: fix static libghostty-vt linking on Windows (#13452)

This PR fixes static linking for libghostty-vt on Windows by propagating
a couple of missing dependencies (discovered while running Neovim's Zig
build, see [this CI
run](https://github.com/neovim/neovim/actions/runs/30130848061/job/89604799965?pr=39773)).

.github/workflows/test.yml

@@ -742,6 +742,10 @@ jobs:
       - name: Build libghostty-vt
         run: zig build -Demit-lib-vt
 
+      - name: Test static linking
+        working-directory: example/c-vt-static
+        run: zig build
+
   build-libghostty-windows-gnu:
     runs-on: namespace-profile-ghostty-windows
     timeout-minutes: 45

example/c-vt-static/build.zig

@@ -14,6 +14,7 @@ pub fn build(b: *std.Build) void {
         .root = b.path("src"),
         .files = &.{"main.c"},
     });
+    exe_mod.addCMacro("GHOSTTY_STATIC", "");
 
     // You'll want to use a lazy dependency here so that ghostty is only
     // downloaded if you actually need it.

pkg/highway/build.zig

@@ -99,6 +99,13 @@ pub fn build(b: *std.Build) !void {
             "-fmath-errno",
             "-fno-exceptions",
         });
+    } else if (target.result.abi == .msvc) {
+        try flags.appendSlice(b.allocator, &.{
+            // -fno-autolink also drops UCRT's /alternatename fallback.
+            "-D_Avx2WmemEnabledWeakValue=_Avx2WmemEnabled",
+            "-fno-autolink",
+            "-fno-stack-protector",
+        });
     }
 
     lib.root_module.addCSourceFiles(.{ .flags = flags.items, .files = &.{

pkg/simdutf/build.zig

@@ -50,10 +50,16 @@ pub fn build(b: *std.Build) !void {
 
     if (no_libcxx) {
         try flags.append(b.allocator, "-DSIMDUTF_NO_LIBCXX");
-        if (target.result.abi != .msvc) {
-            // Clang/GCC-only flags; MSVC doesn't accept these.
-            try flags.append(b.allocator, "-fno-exceptions");
-            try flags.append(b.allocator, "-fno-rtti");
+        try flags.append(b.allocator, "-fno-exceptions");
+        try flags.append(b.allocator, "-fno-rtti");
+        if (target.result.abi == .msvc) {
+            try flags.appendSlice(b.allocator, &.{
+                "-D_USE_STD_VECTOR_ALGORITHMS=0",
+                // -fno-autolink also drops UCRT's /alternatename fallback.
+                "-D_Avx2WmemEnabledWeakValue=_Avx2WmemEnabled",
+                "-fno-autolink",
+                "-fno-stack-protector",
+            });
         }
 
         lib.root_module.addCMacro("SIMDUTF_NO_LIBCXX", "1");

src/build/GhosttyLibVt.zig

@@ -247,6 +247,19 @@ fn initLib(
         // Zig's ubsan emits /exclude-symbols linker directives that
         // are incompatible with the MSVC linker (LNK4229).
         lib.bundle_ubsan_rt = false;
+
+        if (kind == .static) {
+            if (target.result.abi == .msvc) {
+                // Zig's compiler runtime doesn't provide MSVC's security
+                // cookie symbols when libc is linked. Disable stack-protector
+                // generation so static consumers don't need BufferOverflowU.
+                lib.root_module.stack_protector = false;
+            }
+
+            // The Zig standard library uses NT and kernel32 symbols.
+            lib.root_module.linkSystemLibrary("ntdll", .{});
+            lib.root_module.linkSystemLibrary("kernel32", .{});
+        }
     }
 
     if (lib.rootModuleTarget().abi.isAndroid()) {

src/build/SharedDeps.zig

@@ -991,6 +991,11 @@ pub fn addSimd(
             "-fno-sanitize=undefined",
             "-fno-sanitize-trap=undefined",
         });
+        if (target.result.abi == .msvc) try flags.appendSlice(b.allocator, &.{
+            // -fno-autolink also drops UCRT's /alternatename fallback.
+            "-D_Avx2WmemEnabledWeakValue=_Avx2WmemEnabled",
+            "-fno-autolink",
+        });
 
         m.addCSourceFiles(.{
             .files = &.{

src/lib_vt.zig

@@ -141,10 +141,25 @@ pub const unicode = struct {
     pub const graphemeWidth = unicode_pkg.graphemeWidth;
 };
 
+/// Used for MSVC builds (see below)
+var msvc_fltused: c_int = 1;
+
 comptime {
     // If we're building the C library (vs. the Zig module) then
     // we want to reference the C API so that it gets exported.
     if (@import("root") == lib) {
+        // MSVC requires this marker whenever floating-point code is present.
+        // Zig's compiler_rt only provides it when libc is not linked.
+        if (builtin.os.tag == .windows and
+            builtin.abi == .msvc and
+            builtin.link_mode == .static)
+        {
+            @export(
+                &msvc_fltused,
+                .{ .name = "_fltused" },
+            );
+        }
+
         // Force-reference our memset override so its export is
         // emitted. This must stay inside the root guard so that
         // downstream Zig module consumers don't get the override