Add x86-alex-pgo-release.
Add x86-alex-pgo-release.

BUG=chromium:226070
TEST=cbuildbot_config_unittest.py

Change-Id: I7dd75a63aeea44f7fcf2f17ef17b44e5e8fa66ff
Reviewed-on: https://gerrit.chromium.org/gerrit/47301
Commit-Queue: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>
Reviewed-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>
Tested-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>

bpsinc-native/src_third_party_chromite,bpsinc-native/src_third_party_chromite,bpsinc-native/src_third_party_chromite,chadversary/chromiumos.chromite,chadversary/chromiumos.chromite