Save kernel autoconf options in a cache file

We're getting enough autoconf tests now that it's a significant chunk of
the build time.  Adding this cache shaves several seconds off for me.

	* hash.cxx (find_hash): Compute a separate script-independent hash
	for caching autoconf values, saved in session.stapconf_path.
	* buildrun.cxx (compile_pass): Tweak the Makefile to read/save
	the autoconf values in the cache directory

1 files changed, 1 insertions, 0 deletions

diff --git a/session.h b/session.h
index 9a28c936..c55310d3 100644
--- a/session.h
+++ b/session.h
@@ -112,6 +112,7 @@ struct systemtap_session
   bool use_cache;
   std::string cache_path;
   std::string hash_path;
+  std::string stapconf_path;
 
   // dwarfless operation
   bool consult_symtab;