distrib/zlib-1.2.8: Build as static libraries.

This small patches adds specific static library module
declarations for our zlib sources. This will be used later
as dependencies for the test programs of additional third-party
libraries like libsparse.

Change-Id: I45164dc067ea165aa78d091fbae8572297a386d8
diff --git a/Makefile.common b/Makefile.common
index 2a077bf..5844245 100644
--- a/Makefile.common
+++ b/Makefile.common
@@ -90,9 +90,7 @@
 #
 ZLIB_DIR := distrib/zlib-1.2.8
 include $(LOCAL_PATH)/$(ZLIB_DIR)/sources.make
-EMULATOR_COMMON_CFLAGS += -I$(LOCAL_PATH)/$(ZLIB_DIR)
-
-common_LOCAL_SRC_FILES += $(ZLIB_SOURCES)
+EMULATOR_COMMON_CFLAGS += -I$(ZLIB_INCLUDES)
 
 ###########################################################
 # GLib sources