[cc/pgo] Mark pgo.sampling property as an arch-variant

Bug: http://b/189438896

This allows disabling sampling PGO for some arches.

Test: Build this topic.
Change-Id: Ib6ddca6685c2e53092afd440ad95ec42d3a9538b
Merged-In: Ib6ddca6685c2e53092afd440ad95ec42d3a9538b
(cherry picked from commit 19a5aae35e36cb45599c3203a233f6a757456a94)
diff --git a/cc/pgo.go b/cc/pgo.go
index 95c9c2e..e78549e 100644
--- a/cc/pgo.go
+++ b/cc/pgo.go
@@ -56,7 +56,7 @@
 type PgoProperties struct {
 	Pgo struct {
 		Instrumentation    *bool
-		Sampling           *bool
+		Sampling           *bool   `android:"arch_variant"`
 		Profile_file       *string `android:"arch_variant"`
 		Benchmarks         []string
 		Enable_profile_use *bool `android:"arch_variant"`