scanner: Guard interface declarations

This allows to include client and server headers in the same file
fixing warnings like

In file included from ../subprojects/wlroots/include/wlr/types/wlr_layer_shell_v1.h:16,
                 from ../src/desktop.h:16,
                 from ../src/server.h:13,
                 from ../tests/testlib.c:8:
tests/59830eb@@footest@sta/wlr-layer-shell-unstable-v1-protocol.h:80:34: warning: redundant redeclaration of ‘zwlr_layer_shell_v1_interface’ [-Wredundant-decls]
   80 | extern const struct wl_interface zwlr_layer_shell_v1_interface;
      |                                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from ../tests/testlib.h:8,
                 from ../tests/testlib.c:7:
tests/59830eb@@footest@sta/wlr-layer-shell-unstable-v1-client-protocol.h:77:34: note: previous declaration of ‘zwlr_layer_shell_v1_interface’ was here
   77 | extern const struct wl_interface zwlr_layer_shell_v1_interface;
      |                                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from ../subprojects/wlroots/include/wlr/types/wlr_layer_shell_v1.h:16,
                 from ../src/desktop.h:16,
                 from ../src/server.h:13,
                 from ../tests/testlib.c:8:
tests/59830eb@@footest@sta/wlr-layer-shell-unstable-v1-protocol.h:106:34: warning: redundant redeclaration of ‘zwlr_layer_surface_v1_interface’ [-Wredundant-decls]
  106 | extern const struct wl_interface zwlr_layer_surface_v1_interface;
      |                                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from ../tests/testlib.h:8,
                 from ../tests/testlib.c:7:
tests/59830eb@@footest@sta/wlr-layer-shell-unstable-v1-client-protocol.h:103:34: note: previous declaration of ‘zwlr_layer_surface_v1_interface’ was here
  103 | extern const struct wl_interface zwlr_layer_surface_v1_interface;

Signed-off-by: Guido Günther <agx@sigxcpu.org>
Closes: #158

1 files changed, 3 insertions, 0 deletions

diff --git a/tests/data/small-client-core.h b/tests/data/small-client-core.h
index c85cca6..d424757 100644
--- a/tests/data/small-client-core.h
+++ b/tests/data/small-client-core.h
@@ -46,6 +46,8 @@ struct another_intf;
 struct intf_A;
 struct intf_not_here;
 
+#ifndef INTF_A_INTERFACE
+#define INTF_A_INTERFACE
 /**
  * @page page_iface_intf_A intf_A
  * @section page_iface_intf_A_desc Description
@@ -60,6 +62,7 @@ struct intf_not_here;
  * A useless example trying to tickle the scanner.
  */
 extern const struct wl_interface intf_A_interface;
+#endif
 
 #ifndef INTF_A_FOO_ENUM
 #define INTF_A_FOO_ENUM