Pass "-Xgc:CMC" to dex2oat when userfaultfd GC is enabled.

This change is a no-op change. It doesn't enable userfaultfd GC by
default. ENABLE_UFFD_GC=true can be passed to the build system to enable
userfaultfd GC for testing purposes.

Bug: 242553398
Test: -
  1. lunch aosp_oriole-userdebug
  2. ENABLE_UFFD_GC=true m
  3. See "--runtime-arg -Xgc:CMC" in .invocation files.
Change-Id: I789b49a71b9604fd41bf1ef77d0ac5bac4cbdf25
diff --git a/dexpreopt/dexpreopt.go b/dexpreopt/dexpreopt.go
index fdfd22e..e3404a5 100644
--- a/dexpreopt/dexpreopt.go
+++ b/dexpreopt/dexpreopt.go
@@ -495,6 +495,10 @@
 		cmd.FlagWithInput("--profile-file=", profile)
 	}
 
+	if global.EnableUffdGc {
+		cmd.Flag("--runtime-arg").Flag("-Xgc:CMC")
+	}
+
 	rule.Install(odexPath, odexInstallPath)
 	rule.Install(vdexPath, vdexInstallPath)
 }