use ctx.os.arch to get architecture

go/private/sdk.bzl

@@ -237,12 +237,6 @@ def _sdk_build_file(ctx, platform):
         },
     )
 
-def _get_env_var(ctx, name, default = ""):
-    if name in ctx.os.environ:
-        return ctx.os.environ[name]
-    else:
-        return default
-
 def _detect_host_platform(ctx):
     if ctx.os.name == "linux":
         goos, goarch = "linux", "amd64"
@@ -282,11 +276,11 @@ def _detect_host_platform(ctx):
         # Default to amd64 when uname doesn't return a known value.
 
     elif ctx.os.name.startswith("windows"):
-        goos, goarch = "windows", "amd64"
-        if _get_env_var(ctx, "PROCESSOR_ARCHITECTURE") == "ARM64":
-            goarch = "arm64"
-        elif _get_env_var(ctx, "PROCESSOR_ARCHITEW6432") == "ARM64":
+        goos = "windows"
+        if ctx.os.arch == "aarch64":
             goarch = "arm64"
+        else:
+            goarch = "amd64"
     elif ctx.os.name == "freebsd":
         goos, goarch = "freebsd", "amd64"
     else: