Add a coverage suffix to avoid Ninja file regeneration.

This CL uses the environment variable, EMMA_INSTRUMENT to determine whether or not coverage is enabled. If coverage is enabled, it adds a bunch of suffixes to the files generated in out/soong/ folders.

This change reduces the build time by avoiding ninja regeneration when users simply switches from atest to atest --experimental-coverage, or vice versa, and no Android.bp changes are made.

Bug: 331444846
Test: Locally run m libc, and then EMMA_INSTRUMENT m libc twice, no ninja regenerations required. Compared the hash of out/target/product/vsoc_x86_64/ between the before-change repo and after-change repo. Only diff is the after-change directory contains an extra file `out/target/product/vsoc_x86_64/.installable_files` while the original directory has only `out/target/product/vsoc_x86_64/.installable_files.previous`, both files have the same hash.
Change-Id: I972aec20a9d97b223cc833ee245016ac4b0f09a2
diff --git a/ui/build/kati.go b/ui/build/kati.go
index a0efd2c..5743ff7 100644
--- a/ui/build/kati.go
+++ b/ui/build/kati.go
@@ -41,7 +41,7 @@
 // arguments.
 func genKatiSuffix(ctx Context, config Config) {
 	// Construct the base suffix.
-	katiSuffix := "-" + config.TargetProduct()
+	katiSuffix := "-" + config.TargetProduct() + config.CoverageSuffix()
 
 	// Append kati arguments to the suffix.
 	if args := config.KatiArgs(); len(args) > 0 {