add dynamic library interface to enable testing

Add interface defining the methods for dynamic linking to enable
testing.

Change-Id: If4d090d3cedc019b426435a1f651191803bfc1a9
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/Makefile.am b/Makefile.am
index c0cbffb..08f5235 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -8,7 +8,9 @@
 	manager.cpp \
 	process.cpp \
 	crc.cpp \
-	utils.cpp
+	utils.cpp \
+	internal/sys.cpp \
+	fs.cpp
 
 libblobcmds_la_LDFLAGS = \
 	$(SYSTEMD_LIBS) \