main.mk: Set dalvik.vm.stack-trace-dir

... instead of dalvik.vm.stack-trace-file. Turns on the new
stack dumping scheme. Each dump is now output to a separate file.

Bug: 32064548
Test: Manual, unit tests included in other components.
Change-Id: I762b09148786e8533fd285d5bae0121ed46dfbe0
diff --git a/core/main.mk b/core/main.mk
index b50e0e7..5b0e55c 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -313,7 +313,7 @@
 
 # Sets the location that the runtime dumps stack traces to when signalled
 # with SIGQUIT. Stack trace dumping is turned on for all android builds.
-ADDITIONAL_BUILD_PROPERTIES += dalvik.vm.stack-trace-file=/data/anr/traces.txt
+ADDITIONAL_BUILD_PROPERTIES += dalvik.vm.stack-trace-dir=/data/anr
 
 # ------------------------------------------------------------
 # Define a function that, given a list of module tags, returns