build: fix static libghostty-vt linking on Windows

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
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.

src/build/GhosttyLibVt.zig

@@ -247,6 +247,14 @@ 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) {
+            // compiler_rt expects ntdll to provide _fltused when libc is
+            // linked, and the Zig standard library uses other NT and kernel32
+            // symbols.
+            lib.root_module.linkSystemLibrary("ntdll", .{});
+            lib.root_module.linkSystemLibrary("kernel32", .{});
+        }
     }
 
     if (lib.rootModuleTarget().abi.isAndroid()) {