Turn on new pass manager for PGO projects

With new pass manager, dex2oat benchmark showed 1.61% performance
improvement though binary size saw an increase of 3.37%.

For Googlers, detailed benchmark results are in go/android-pgo-npm.

Test: m checkbuild
Bug: 118894695
Change-Id: I1687886acac7f61e67265a9c73997fb241ad31e6

cc/pgo.go

@@ -27,8 +27,11 @@ import (
 
 var (
 	// Add flags to ignore warnings that profiles are old or missing for
-	// some functions
-	profileUseOtherFlags = []string{"-Wno-backend-plugin"}
+	// some functions, and turn on the experimental new pass manager.
+	profileUseOtherFlags = []string{
+		"-Wno-backend-plugin",
+		"-fexperimental-new-pass-manager",
+	}
 
 	globalPgoProfileProjects = []string{
 		"toolchain/pgo-profiles",