Allow spl_config.h to be included by dependant packages (updated)

We need dependent packages to be able to include spl_config.h to
build properly.  This was partially solved in commit 0cbaeb1 by using
AH_BOTTOM to #undef common #defines (PACKAGE, VERSION, etc) which
autoconf always adds and cannot be easily removed.  This solution
works as long as the spl_config.h is included before your projects
config.h.  That turns out to be easier said than done.  In particular,
this is a problem when your package includes its config.h using the
-include gcc option which ensures the first thing included is your
config.h.

To handle all cases cleanly I have removed the AH_BOTTOM hack and
replaced it with an AC_CONFIG_HEADERS command.  This command runs
immediately after spl_config.h is written and with a little awk-foo
it strips the offending #defines from the file.  This eliminates
the problem entirely and makes header safe for inclusion.

Also in this change I have removed the few places in the code where
spl_config.h is included.  It is now added to the gcc compile line
to ensure the config results are always available.

Finally, I have also disabled the verbose kernel builds.  If you
want them back you can always build with 'make V=1'.  Since things
are working now they don't need to be on by default.

configure.ac

@@ -29,10 +29,12 @@ AC_LANG(C)
 SPL_AC_META
 AC_CONFIG_AUX_DIR([config])
 AC_CANONICAL_SYSTEM
-AM_INIT_AUTOMAKE([$SPL_META_NAME], [$SPL_META_VERSION])
-AC_CONFIG_HEADERS([spl_config.h])
-AH_BOTTOM([#include <spl_unconfig.h>])
 AM_MAINTAINER_MODE
+AM_INIT_AUTOMAKE([$SPL_META_NAME], [$SPL_META_VERSION])
+AC_CONFIG_HEADERS([spl_config.h], [
+	(mv spl_config.h spl_config.h.tmp &&
+	awk -f config/config.awk spl_config.h.tmp >spl_config.h &&
+	rm spl_config.h.tmp) || exit 1])
 
 AC_PROG_INSTALL
 AC_PROG_CC