bolt-gen: add compilation tests

Add a test for checking that the bolt-gens do the right thing
for a fairly exhaustive test case set (and that it compiles).

Note that this doesn't check that we've got the memory assignment
pieces worked out.

It's got a kind of exotic reliance on the update-mocks in that in
order to depend on as little of the wire/ code as possible (we
only import wire/wire.h), we include an AUTOGENERATE comment
in the test_cases CSV file, and then run update-mocks as part of
the build for that file.

tools/test/run-test-wire.c

@@ -0,0 +1,12 @@
+#include "gen_test.c"
+
+#include <assert.h>
+#include <stdio.h>
+
+#include <common/utils.h>
+
+int main(void)
+{
+	setup_locale();
+
+}