[build] Fix false detection of compressed pointers as cross builds.
[build] Fix false detection of compressed pointers as cross builds.

Broken by 3c01efcbb07cb1af8da0e13d8edca79457188062.

TEST=fuzzer
Change-Id: Ifefdd1864de969b82f10471f4184c1169ec9aaba
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/244741
Reviewed-by: Alexander Aprelev <dfb74c35a357c2059971a4bf7fe26b6a7c18085d@google.com>
Commit-Queue: Ryan Macnak <d738b7f001baf9789095d7dc549cff6de60b011d@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk