Makefile: use completely separate spec-derived files for EXPERIMENTAL_FEATURES

This avoids overwriting the ones in git, and generally makes things neater.

We have convenience headers wire/peer_wire.h and wire/onion_wire.h to
avoid most #ifdefs: simply include those.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

devtools/decodemsg.c

@@ -5,8 +5,13 @@
 #include <common/utils.h>
 #include <stdio.h>
 #include <unistd.h>
+#if EXPERIMENTAL_FEATURES
+#include <wire/onion_exp_printgen.h>
+#include <wire/peer_exp_printgen.h>
+#else
 #include <wire/onion_printgen.h>
 #include <wire/peer_printgen.h>
+#endif
 
 int main(int argc, char *argv[])
 {