Add platform-wide sampling PGO option

This causes the compiler to emit some additional debug infomation that
will be used for sampling PGO. These debug infomation will get stripped
so it only affects intermediate files.

Test: build
Bug: 79161490
Bug: 153039105
Change-Id: Ie4d1d5ffbd311ba6e268cb94a618f5272be246ef
Merged-In: Ie4d1d5ffbd311ba6e268cb94a618f5272be246ef
(cherry picked from commit ceb5b76c91)

android/variable.go

@@ -251,6 +251,8 @@ type productVariables struct {
 	ClangTidy  *bool   `json:",omitempty"`
 	TidyChecks *string `json:",omitempty"`
 
+	SamplingPGO  *bool   `json:",omitempty"`
+
 	NativeLineCoverage   *bool    `json:",omitempty"`
 	Native_coverage      *bool    `json:",omitempty"`
 	ClangCoverage        *bool    `json:",omitempty"`