GCC: do not use __has_feature in UnsanitizedAtomic

GCC fails to build as unsanitized_atomic.cc is using a Clang only
compiler macro: __has_feature:

  ../../third_party/blink/renderer/platform/heap/unsanitized_atomic.cc:9:18: error: missing binary operator before token "("
      9 | #if __has_feature(address_sanitizer)
        |                  ^

Bug: 819294
Change-Id: Id1ef4972e61d82739b115398458fd238736de4a9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2052106Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Commit-Queue: José Dapena Paz <jdapena@igalia.com>
Cr-Commit-Position: refs/heads/master@{#740841}

third_party/blink/renderer/platform/heap/unsanitized_atomic.cc

@@ -6,7 +6,9 @@
 
 #include "cstdint"
 
-#if __has_feature(address_sanitizer)
+#include "base/compiler_specific.h"
+
+#if HAS_FEATURE(address_sanitizer)
 #error "Must be built without asan."
 #endif