Revert "Remove zlib"

This reverts commit d874a1fd14.

Conflicts:
* CMakeLists.txt:
  * ENABLE_ZLIB_SUPPORT: there has been a change immediately after
    where it was removed. Just re-add what was removed.
* tests/CMakeLists.txt:
  * ENABLE_ZLIB_SUPPORT: there has been a change immediately after
    where it was removed. Just re-add what was removed.

programs/Makefile

@@ -44,6 +44,11 @@ EXEXT=
 SHARED_SUFFIX=
 endif
 
+# Zlib shared library extensions:
+ifdef ZLIB
+LOCAL_LDFLAGS += -lz
+endif
+
 APPS = \
 	aes/aescrypt2$(EXEXT) \
 	aes/crypt_and_hash$(EXEXT) \

programs/test/CMakeLists.txt

@@ -2,6 +2,10 @@ set(libs
     mbedtls
 )
 
+if(ENABLE_ZLIB_SUPPORT)
+    set(libs ${libs} ${ZLIB_LIBRARIES})
+endif(ENABLE_ZLIB_SUPPORT)
+
 add_executable(selftest selftest.c)
 target_link_libraries(selftest ${libs})