build: avoid MSVC C++ runtime in no-libcxx builds

AI-assisted: Codex

src/build/GhosttyLibVt.zig

@@ -249,9 +249,14 @@ fn initLib(
         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.
+            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", .{});
         }

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 = &.{