move HOST_IPMI_LIB_PATH to configure.ac

Per TODO in Makefile.am, move the definition of HOST_IPMI_LIB_PATH from
the Makefile to the configure script.

Change-Id: If39bf1193f4502c239a78e21487566b234b746f8
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/ipmid.cpp b/ipmid.cpp
index 238c0e5..cfaad9b 100644
--- a/ipmid.cpp
+++ b/ipmid.cpp
@@ -1,3 +1,5 @@
+#include "config.h"
+
 #include "ipmid.hpp"
 
 #include "host-cmd-manager.hpp"