Only package gcno files for gcov coverage builds.

Bug: 154550223
Test: m -j NATIVE_COVERAGE=true droid dist tests
Test: m -j CLANG_COVERAGE=true droid dist tests
Change-Id: I81598bcab8db105de6692156c001fc961409ce63
diff --git a/cc/builder.go b/cc/builder.go
index 136263b..e09dc55 100644
--- a/cc/builder.go
+++ b/cc/builder.go
@@ -293,7 +293,7 @@
 	rsFlags       string
 	toolchain     config.Toolchain
 	tidy          bool
-	coverage      bool
+	gcovCoverage  bool
 	sAbiDump      bool
 	emitXrefs     bool
 
@@ -355,7 +355,7 @@
 		tidyFiles = make(android.Paths, 0, len(srcFiles))
 	}
 	var coverageFiles android.Paths
-	if flags.coverage {
+	if flags.gcovCoverage {
 		coverageFiles = make(android.Paths, 0, len(srcFiles))
 	}
 	var kytheFiles android.Paths
@@ -456,7 +456,7 @@
 
 		var ccCmd string
 		tidy := flags.tidy
-		coverage := flags.coverage
+		coverage := flags.gcovCoverage
 		dump := flags.sAbiDump
 		rule := cc
 		emitXref := flags.emitXrefs