--disable-lz4 --disable-lzo breaks compilation on master

[Gert Döring]

options.c: In function 'options_set_backwards_compatible_options':
options.c:3213:10: warning: implicit declaration of function 'comp_non_stub_enabled' [-Wimplicit-function-declaration]
 3213 |     if (!comp_non_stub_enabled(&o->comp) && !need_compatibility_before(o, 20600)
      |          ^~~~~~~~~~~~~~~~~~~~~
options.c:3213:34: error: 'struct options' has no member named 'comp'
 3213 |     if (!comp_non_stub_enabled(&o->comp) && !need_compatibility_before(o, 20600)
      |                                  ^~
options.c:3214:14: error: 'struct options' has no member named 'comp'
 3214 |         && (o->comp.flags == 0))
      |              ^~
options.c:3216:10: error: 'struct options' has no member named 'comp'
 3216 |         o->comp.flags = COMP_F_ALLOW_STUB_ONLY|COMP_F_ADVERTISE_STUBS_ONLY;
      |          ^~
options.c:3216:25: error: 'COMP_F_ALLOW_STUB_ONLY' undeclared (first use in this function)
 3216 |         o->comp.flags = COMP_F_ALLOW_STUB_ONLY|COMP_F_ADVERTISE_STUBS_ONLY;
      |                         ^~~~~~~~~~~~~~~~~~~~~~

[Gert Döring]

commit 0bc3375f1fff09d21f224eb9f8f9c3943ed4f404
Author: Max Fillinger
Date: Thu Oct 21 13:50:37 2021 +0200

Fix build with compression disabled

[Gert Döring]

MaxF discovered more fallout - with the patch it compiles, but blows up later

10:49 < MaxF> Hi! I'm still having problems when I disable compression in 
              configure. It compiles now, but if I try to test it, I get an 
              error in check_ping_send_dowork
10:50 < MaxF> ... can't copy the error message because my VM is acting up, one 
              moment
10:52 < MaxF> Assertion failed at ../../../openvpn/src/openvpn/ping.c:82 
              (buf_init(&c->c2.buf, FRAME_HEADROOM(&c->c2.frame)))
10:54 < MaxF> The assertion fails because the output from FRAME_HEADROOM is 
              negative. This only happens when I compile with --disable-lz4 and 
              --disable-lzo.

[Gert Döring]

11:46 < MaxF> I just finished a git bisect and this is where it breaks:
​https://github.com/OpenVPN/openvpn/commit/8c72d7981c32c43d1c7967a312bb439e13fc5b40

[Gert Döring]

This was re-tested with yesterday's master (commit e8a2794824ded011a1) and things no longer break - as expected, the "Frame" rewrite fixes all these weird special cases.

Closing this ticket. Thanks for testing.