tools/generate_wire.py: allow generated C files to have includes added.

We previously ignored --include= for these, but onion is about to start
needing bolt12.

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

tools/gen/impl_template

@@ -9,6 +9,9 @@
 #include <ccan/tal/str/str.h>
 #include <common/utils.h>
 #include <stdio.h>
+% for i in includes:
+${i}
+% endfor
 
 #ifndef SUPERVERBOSE
 #define SUPERVERBOSE(...)

tools/gen/print_impl_template

@@ -8,6 +8,9 @@
 #include <common/utils.h>
 #include <inttypes.h>
 #include <stdio.h>
+% for i in includes:
+${i}
+% endfor
 
 % if enum_sets:
 void print${options.enum_name}_message(const u8 *msg)