Add gcc_demangle to BUILD_TINY_ANDROID projects

libgccdemangle.so is required to build libcorkscrew, which is in
system/core and built when BUILD_TINY_ANDROID is set.

Change-Id: Ide9af58cfc075e27a7368993b29be2c0e53275a8
diff --git a/core/main.mk b/core/main.mk
index 506cd4f..3098051 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -416,6 +416,7 @@
 	build/libs \
 	build/target \
 	build/tools/acp \
+	external/gcc-demangle \
 	external/mksh \
 	external/yaffs2 \
 	external/zlib