Add support for PB_ENABLE_MALLOC in nanopb-c

There will be two version of the the nanopb-c library,
libnanopb-c-2.8.0 which doesn't support automatic malloc
and libnanopb-c-2.8.0-enable_malloc which does.

There will be two version of the the nanopb-c library,
libnanopb-c-2.8.0 which doesn't support automatic malloc
and libnanopb-c-2.8.0-enable_malloc which does.

Set LOCAL_PROTO_OPTIMIZE_TYPE=nanopb-c which doesn't support
malloc and set it to nanopb-c-enable_malloc which does.

For client code details see nanopb-api:
  http://koti.kapsi.fi/jpa/nanopb/docs/reference.html

Change-Id: If238412463aabb5e1d556dfc9c464bcaf9e3333a
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index 81c54eb..605908d 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -125,7 +125,7 @@
 LOCAL_DEX_PREOPT:= # '',true,false,nostripping
 LOCAL_DEX_PREOPT_IMAGE_LOCATION:=
 LOCAL_DEX_PREOPT_FLAGS:=
-LOCAL_PROTOC_OPTIMIZE_TYPE:= # lite(default),micro,nano,full,nanopb-c
+LOCAL_PROTOC_OPTIMIZE_TYPE:= # lite(default),micro,nano,full,nanopb-c,nanopb-c-enable_malloc
 LOCAL_PROTOC_FLAGS:=
 LOCAL_PROTO_JAVA_OUTPUT_PARAMS:=
 LOCAL_NO_CRT:=