Build module from source branch instead of using prebuilds when coverage is enabled.

Test: successfully get coverage data from coverage build.
Bug: 137865099
Change-Id: I7df96c2b2c2ec2859393fb2c19ffe1081d112c96
diff --git a/apex/apex.go b/apex/apex.go
index 0466ccb..330724d 100644
--- a/apex/apex.go
+++ b/apex/apex.go
@@ -1474,6 +1474,10 @@
 	// to build the prebuilts themselves.
 	forceDisable = forceDisable || ctx.Config().UnbundledBuild()
 
+	// Force disable the prebuilts when coverage is enabled.
+	forceDisable = forceDisable || ctx.DeviceConfig().NativeCoverageEnabled()
+	forceDisable = forceDisable || ctx.Config().IsEnvTrue("EMMA_INSTRUMENT")
+
 	// b/137216042 don't use prebuilts when address sanitizer is on
 	forceDisable = forceDisable || android.InList("address", ctx.Config().SanitizeDevice()) ||
 		android.InList("hwaddress", ctx.Config().SanitizeDevice())