Update build.ps1 (dotnet#97982)

* Update build.ps1

* Update build.ps1

eng/build.ps1

@@ -147,6 +147,26 @@ if ($os) {
   $os = $os.ToLowerInvariant()
 }
 
+if ($os -eq "browser") {
+  # override default arch for Browser, we only support wasm
+  $arch = "wasm"
+
+  if ($msbuild -eq $True) {
+    Write-Error "Using the -msbuild option isn't supported when building for Browser on Windows, we need need ninja for Emscripten."
+    exit 1
+  }
+}
+
+if ($os -eq "wasi") {
+  # override default arch for wasi, we only support wasm
+  $arch = "wasm"
+
+  if ($msbuild -eq $True) {
+    Write-Error "Using the -msbuild option isn't supported when building for WASI on Windows, we need ninja for WASI-SDK."
+    exit 1
+  }
+}
+
 if ($vs) {
   $archToOpen = $arch[0]
   $configToOpen = $configuration[0]
@@ -247,6 +267,16 @@ if ($vs) {
     $env:RUNTIMEFLAVOR=$runtimeFlavor
   }
 
+  # Respect the TargetOS variable for building non AnyOS libraries
+  if ($os) {
+    $env:TARGETOS=$os
+  }
+
+  # Respect the TargetArchitecture variable for building non AnyCPU libraries
+  if ($arch) {
+    $env:TARGETARCHITECTURE=$arch
+  }
+
   # Launch Visual Studio with the locally defined environment variables
   ."$vs"
 
@@ -301,26 +331,6 @@ $env:DOTNETSDK_ALLOW_TARGETING_PACK_CACHING=0
 
 $failedBuilds = @()
 
-if ($os -eq "browser") {
-  # override default arch for Browser, we only support wasm
-  $arch = "wasm"
-
-  if ($msbuild -eq $True) {
-    Write-Error "Using the -msbuild option isn't supported when building for Browser on Windows, we need need ninja for Emscripten."
-    exit 1
-  }
-}
-
-if ($os -eq "wasi") {
-  # override default arch for wasi, we only support wasm
-  $arch = "wasm"
-
-  if ($msbuild -eq $True) {
-    Write-Error "Using the -msbuild option isn't supported when building for WASI on Windows, we need ninja for WASI-SDK."
-    exit 1
-  }
-}
-
 foreach ($config in $configuration) {
   $argumentsWithConfig = $arguments + " -configuration $((Get-Culture).TextInfo.ToTitleCase($config))";
   foreach ($singleArch in $arch) {