Support for jemalloc to replace dlmalloc.

To use jemalloc, add MALLOC_IMPL = jemalloc in a board config file
and you get the new version automatically.

Update the pthread_create_key tests since jemalloc uses a few keys.
Add a new test to verify memalign works as expected.

Bug: 981363

Change-Id: I16eb152b291a95bd2499e90492fc6b4bd7053836
diff --git a/tests/Android.mk b/tests/Android.mk
index 51f10ca..37aeec3 100644
--- a/tests/Android.mk
+++ b/tests/Android.mk
@@ -40,6 +40,10 @@
 
 test_cflags += -D__STDC_LIMIT_MACROS  # For glibc.
 
+ifeq ($(MALLOC_IMPL),jemalloc)
+test_cflags += -DUSE_JEMALLOC
+endif
+
 test_cppflags = \
     -std=gnu++11 \