applypatch: Forward declare struct Value.

And move '#include "edify/expr.h"' into .cpp files. This breaks the
transitive dependency on libedify. Modules that include
"applypatch/applypatch.h" don't need to add libedify into their
dependency list, unless they really need anything from libedify.

Build libedify static library for host, which is needed by
libimgpatch.

Test: mmma bootable/recovery
Change-Id: Ibb53d322579fcbf593438d058d9bcee240625941

applypatch/Android.mk

@@ -53,6 +53,7 @@ LOCAL_C_INCLUDES := \
     bootable/recovery
 LOCAL_EXPORT_C_INCLUDE_DIRS := $(LOCAL_PATH)/include
 LOCAL_STATIC_LIBRARIES := \
+    libedify \
     libcrypto \
     libbspatch \
     libbase \
@@ -77,6 +78,7 @@ LOCAL_C_INCLUDES := \
     bootable/recovery
 LOCAL_EXPORT_C_INCLUDE_DIRS := $(LOCAL_PATH)/include
 LOCAL_STATIC_LIBRARIES := \
+    libedify \
     libcrypto \
     libbspatch \
     libbase \