Compare generated cache file with existing cache file

Bug: b/292128421
Test: Create a aconfig declartion file with only package name
but no flags. Then build the corresponding java library.

Change-Id: I7e9d09d5488eb9c95784fd486d3a9107539412a4

aconfig/init.go

@@ -30,7 +30,7 @@ var (
 				` ${declarations}` +
 				` ${values}` +
 				` --cache ${out}.tmp` +
-				` && ( if cmp -s ${out}.tmp ; then rm ${out}.tmp ; else mv ${out}.tmp ${out} ; fi )`,
+				` && ( if cmp -s ${out}.tmp ${out} ; then rm ${out}.tmp ; else mv ${out}.tmp ${out} ; fi )`,
 			//				` --build-id ${release_version}` +
 			CommandDeps: []string{
 				"${aconfig}",