configure: Add missing include/mk/config-openposix.mk reference

The file include/mk/config-openposix.mk should be added to the
AUTOGENERATED_FILES array in include/mk/automake.mk so that it can be
cleaned in the cleaning targets. Also, add a small comment in configure.ac
so it does not happen again.

Link: https://lore.kernel.org/ltp/20250327-fix_make_clean-v1-1-8b9ed2a8d96a@suse.com/
Fixes: 63b6532 ("open_posix_testsuite: Propagate configure params")
Reviewed-by: Cyril Hrubis <chrubis@suse.cz>
Reviewed-by: Petr Vorel <pvorel@suse.cz>
Signed-off-by: Ricardo B. Marlière <rbm@suse.com>

Author: rbmarliere

configure.ac

@@ -7,6 +7,8 @@ AC_CONFIG_AUX_DIR([.])
 AM_INIT_AUTOMAKE
 AC_CONFIG_HEADERS([include/config.h])
 AC_CONFIG_MACRO_DIR([m4])
+
+# Adding files here? Please update include/mk/automake.mk
 AC_CONFIG_FILES([ \
     include/mk/config.mk \
     include/mk/config-openposix.mk \

include/mk/automake.mk

@@ -76,6 +76,7 @@ ac-maintainer-clean:: ac-distclean
 #
 AUTOGENERATED_FILES	= \
 			include/mk/config.mk	\
+			include/mk/config-openposix.mk \
 			include/mk/features.mk	\
 			lib/ltp.pc		\
 			m4/Makefile