Use the TMPDIR environment variable for test directory if set.

Bug: 16499668

Change-Id: I7da5559c13597d7bca4e4037a1e9335f0b6d8230
diff --git a/build/Android.common_path.mk b/build/Android.common_path.mk
index 8c0d9f2..bd1e8aa 100644
--- a/build/Android.common_path.mk
+++ b/build/Android.common_path.mk
@@ -31,7 +31,11 @@
 ART_TARGET_TEST_OUT := $(TARGET_OUT_DATA)/art-test
 
 # Directory used for temporary test files on the host.
+ifneq ($(TMPDIR),)
+ART_HOST_TEST_DIR := $(TMPDIR)/test-art-$(shell echo $$PPID)
+else
 ART_HOST_TEST_DIR := /tmp/test-art-$(shell echo $$PPID)
+endif
 
 # Core.oat location on the device.
 TARGET_CORE_OAT := $(ART_TARGET_TEST_DIR)/$(DEX2OAT_TARGET_ARCH)/core.oat