Add new source files to build.

Test: make checkbuild
Bug: https://github.com/android-ndk/ndk/issues/216
Change-Id: I6b72dd9a2ac81f06040666858673b35f08b00466
diff --git a/Android.bp b/Android.bp
index e8eddbe..d9e8617 100644
--- a/Android.bp
+++ b/Android.bp
@@ -34,6 +34,7 @@
         "src/cxa_vector.cpp",
         "src/cxa_virtual.cpp",
         "src/exception.cpp",
+        "src/fallback_malloc.cpp",
         "src/private_typeinfo.cpp",
         "src/stdexcept.cpp",
         "src/typeinfo.cpp",