Fix build.

Change-Id: I5a35eee4074e35f459c86c7f9b1d9b0754888940
diff --git a/libc/Android.mk b/libc/Android.mk
index 543b4b4..299a46d 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -505,7 +505,7 @@
 else
   libc_common_cflags += -DUSE_DLMALLOC
 
-  libc_malloc_src := bionic/dlmalloc.cpp
+  libc_malloc_src := bionic/dlmalloc.c
 endif
 
 # To customize dlmalloc's alignment, set BOARD_MALLOC_ALIGNMENT in