base/task: Use BUILDFLAG for OS checking

Use BUILDFLAG(IS_XXX) instead of defined(OS_XXX).

Generated by `os_buildflag_migration.py` (https://crrev.com/c/3311983).

[email protected]

Bug: 1234043
Test: No functionality change
Change-Id: I1b3a70b4cb0e097816d962f6434b1f8bf4e010a5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3391090
Reviewed-by: Nico Weber <[email protected]>
Commit-Queue: Nico Weber <[email protected]>
Cr-Commit-Position: refs/heads/main@{#959626}
diff --git a/base/task/task_features.h b/base/task/task_features.h
index 48df3de0..5ff7e41 100644
--- a/base/task/task_features.h
+++ b/base/task/task_features.h
@@ -48,7 +48,7 @@
 extern const BASE_EXPORT base::FeatureParam<WakeUpStrategy>
     kWakeUpStrategyParam;
 
-#if defined(OS_WIN) || defined(OS_APPLE)
+#if BUILDFLAG(IS_WIN) || BUILDFLAG(IS_APPLE)
 #define HAS_NATIVE_THREAD_POOL() 1
 #else
 #define HAS_NATIVE_THREAD_POOL() 0