Add USE_FILESLIST_GO to switch to fileslist.go

fileslist.go is still disabled by default.  To enable, use:
USE_FILESLIST_GO=true m -j

Bug: 36274890
Test: Manual, with m -j

Change-Id: I722e17fa7fb6ba91e2b2c44cd7524d974cbe4a56
(cherry picked from commit 9fe97e231b7d7954a16647ea72d01d750265dc8b)
diff --git a/core/config.mk b/core/config.mk
index 319a069..9c93240 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -497,6 +497,7 @@
 
 SOONG_ZIP := $(SOONG_HOST_OUT_EXECUTABLES)/soong_zip
 ZIP2ZIP := $(SOONG_HOST_OUT_EXECUTABLES)/zip2zip
+FILESLIST := $(SOONG_HOST_OUT_EXECUTABLES)/fileslist
 
 JAVAC_FILTER := $(SOONG_HOST_OUT_EXECUTABLES)/soong_javac_filter