build: skip linkLibCpp on MSVC targets

Zig's bundled libc++/libc++abi conflicts with the MSVC C++ runtime
headers (vcruntime_typeinfo.h, vcruntime_exception.h, etc.) when
targeting native-native-msvc. This caused compilation failures in
the SIMD C++ code due to -nostdinc++ suppressing MSVC headers and
libc++ types clashing with MSVC runtime types.

Skip linkLibCpp() for MSVC targets across all packages (highway,
simdutf, utfcpp) and the main build (SharedDeps, GhosttyZig) since
MSVC provides its own C++ standard library natively. Also add
missing <iterator> and <cstddef> includes that were previously
pulled in transitively through libc++ headers but are not
guaranteed by MSVC's headers.

pkg/highway/build.zig

@@ -20,7 +20,11 @@ pub fn build(b: *std.Build) !void {
         }),
         .linkage = .static,
     });
-    lib.linkLibCpp();
+    // On MSVC, the C++ standard library is provided by the MSVC runtime
+    // and linking Zig's bundled libc++ would conflict with it.
+    if (target.result.abi != .msvc) {
+        lib.linkLibCpp();
+    }
     if (upstream_) |upstream| {
         lib.addIncludePath(upstream.path(""));
         module.addIncludePath(upstream.path(""));

pkg/simdutf/build.zig

@@ -12,7 +12,11 @@ pub fn build(b: *std.Build) !void {
         }),
         .linkage = .static,
     });
-    lib.linkLibCpp();
+    // On MSVC, the C++ standard library is provided by the MSVC runtime
+    // and linking Zig's bundled libc++ would conflict with it.
+    if (target.result.abi != .msvc) {
+        lib.linkLibCpp();
+    }
     lib.addIncludePath(b.path("vendor"));
 
     if (target.result.os.tag.isDarwin()) {

pkg/utfcpp/build.zig

@@ -12,7 +12,11 @@ pub fn build(b: *std.Build) !void {
         }),
         .linkage = .static,
     });
-    lib.linkLibCpp();
+    // On MSVC, the C++ standard library is provided by the MSVC runtime
+    // and linking Zig's bundled libc++ would conflict with it.
+    if (target.result.abi != .msvc) {
+        lib.linkLibCpp();
+    }
 
     if (target.result.os.tag.isDarwin()) {
         const apple_sdk = @import("apple_sdk");

src/build/GhosttyZig.zig

@@ -64,8 +64,10 @@ fn initVt(
         .optimize = cfg.optimize,
 
         // SIMD require libc/libcpp (both) but otherwise we don't care.
+        // On MSVC, the C++ standard library is provided by the MSVC runtime
+        // and linking libc++ would conflict with it.
         .link_libc = if (cfg.simd) true else null,
-        .link_libcpp = if (cfg.simd) true else null,
+        .link_libcpp = if (cfg.simd and cfg.target.result.abi != .msvc) true else null,
     });
     vt.addOptions("build_options", general_options);
     vt_options.add(b, vt);

src/build/SharedDeps.zig

@@ -399,8 +399,12 @@ pub fn add(
         step.addIncludePath(b.path("src/apprt/gtk"));
     }
 
-    // libcpp is required for various dependencies
-    step.linkLibCpp();
+    // libcpp is required for various dependencies. On MSVC, the C++
+    // standard library is provided by the MSVC runtime and linking
+    // libc++ would conflict with it.
+    if (step.rootModuleTarget().abi != .msvc) {
+        step.linkLibCpp();
+    }
 
     // We always require the system SDK so that our system headers are available.
     // This makes things like `os/log.h` available for cross-compiling.

src/simd/codepoint_width.cpp

@@ -6,6 +6,7 @@
 #include <hwy/print-inl.h>
 
 #include <cassert>
+#include <iterator>
 
 HWY_BEFORE_NAMESPACE();
 namespace ghostty {

src/simd/index_of.h

@@ -6,6 +6,8 @@
 #endif
 
 #include <hwy/highway.h>
+
+#include <cstddef>
 #include <optional>
 
 HWY_BEFORE_NAMESPACE();