Add C11 <stdatomic.h>.

Bug: 14903517
Change-Id: I631dbfdaa698cf7fea8e3b5e18a32586383e62a5
diff --git a/tests/Android.mk b/tests/Android.mk
index 37aeec3..d753acc 100644
--- a/tests/Android.mk
+++ b/tests/Android.mk
@@ -87,6 +87,7 @@
     stack_protector_test.cpp \
     stack_unwinding_test.cpp \
     stack_unwinding_test_impl.c \
+    stdatomic_test.cpp \
     stdint_test.cpp \
     stdio_test.cpp \
     stdlib_test.cpp \