From 0196080358dc1821d0eede8031f040fa0f458efb Mon Sep 17 00:00:00 2001
From: Dylan Conway <dylan.conway567@gmail.com>
Date: Mon, 9 Mar 2026 22:05:29 -0700
Subject: [PATCH 1/2] Build ICU stage 2 with ClangCL so -march limits codegen
 on x64

---
 build-icu.ps1 | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/build-icu.ps1 b/build-icu.ps1
index 2ceca7608c55..106f0cd896b3 100644
--- a/build-icu.ps1
+++ b/build-icu.ps1
@@ -76,11 +76,14 @@ if (-not (Test-Path $ICU_SOURCE_DIR)) {
 }
 
 if ($Platform -eq "x64") {
-    $ArchFlag = if ($Baseline) { "/arch:SSE2" } else { "/arch:AVX2" }
+    $ArchFlag = if ($Baseline) { "/clang:-march=nehalem" } else { "/clang:-march=haswell" }
 } else {
     $ArchFlag = ""
 }
 
+# ClangCL for stage 2 so -march= limits codegen (MSVC /arch:SSE2 is a no-op on x64).
+$ToolsetArg = if ($Platform -eq "x64") { @("/p:PlatformToolset=ClangCL") } else { @() }
+
 # --- Function to patch vcxproj files for static library build with /MT ---
 function Patch-IcuVcxProj {
     param(
@@ -235,6 +238,7 @@ foreach ($target in @("common", "i18n")) {
         "/v:minimal"
     )
 
+    $buildArgs += $ToolsetArg
     & $msbuildPath $buildArgs
 
     if ($LASTEXITCODE -ne 0) {

From 335daa86527e86bd414a45eba2cce35eb571a6f6 Mon Sep 17 00:00:00 2001
From: Dylan Conway <dylan.conway567@gmail.com>
Date: Mon, 9 Mar 2026 22:14:02 -0700
Subject: [PATCH 2/2] Strip .rc from ICU vcxproj since rc.exe cannot parse
 clang stddef.h

---
 build-icu.ps1 | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/build-icu.ps1 b/build-icu.ps1
index 106f0cd896b3..338b3d368a96 100644
--- a/build-icu.ps1
+++ b/build-icu.ps1
@@ -128,6 +128,10 @@ function Patch-IcuVcxProj {
     $content = $content -replace '<OutputFile>[^<]*\.(dll|DLL)</OutputFile>', ''
     $content = $content -replace '<ImportLibrary>[^<]*</ImportLibrary>', ''
 
+    # Strip .rc — rc.exe cannot parse clang stddef.h and static libs do not need version resources.
+    $content = $content -replace "(?s)<ResourceCompile[^>]*>.*?</ResourceCompile>", ""
+    $content = $content -replace "<ResourceCompile[^>]*/>", ""
+
     # For stubdata - remove resource-only DLL settings
     if ($FilePath -match "stubdata") {
         $content = $content -replace '<NoEntryPoint>true</NoEntryPoint>', ''