Implement LOCAL_COMPRESSED_MODULE.

- Prebuilts with LOCAL_MODULE_CLASS == APPS and BUILD_PACKAGE that
  define LOCAL_COMPRESSED_MODULE := true will be installed compressed
  in the system partition.
- The compression algorithm is simple gzip for now.

In addition :
- Compressed modules are not dex-preopted.
- JNI shared libraries are always embedded inside compressed modules,
  they are never installed as separate files on the FS.

Test: Manual
Bug: 63802184

Change-Id: Id12b1ff0b1d68791ec1178783f7e78910e122a33
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index 1fba952..a687866 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -34,6 +34,7 @@
 LOCAL_CLASSPATH:=
 LOCAL_COMPATIBILITY_SUITE:=
 LOCAL_COMPATIBILITY_SUPPORT_FILES:=
+LOCAL_COMPRESSED_MODULE:=
 LOCAL_CONLYFLAGS:=
 LOCAL_COPY_HEADERS:=
 LOCAL_COPY_HEADERS_TO:=