Add Linux Test eXecutor inside tools

The ltx program runs on the system under test (SUT). It's primary
purpose is to run test executables in parallel and serialise the
results.

Acked-by: Richard Palethorpe <rpalethorpe@suse.com>
Reviewed-by: Petr Vorel <pvorel@suse.cz>
Reviewed-by: Cyril Hrubis <chrubis@suse.cz>
Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>
[ pvorel: Add Subproject commit 7e397fe1a2d34a100c7dbfa452bd5d86ca1ddb77 ]
Signed-off-by: Petr Vorel <pvorel@suse.cz>

Author: acerv

.gitmodules

@@ -7,3 +7,6 @@
 [submodule "tools/kirk"]
 	path = tools/kirk
 	url = https://github.com/linux-test-project/kirk.git
+[submodule "tools/ltx/ltx-src"]
+	path = tools/ltx/ltx-src
+	url = https://github.com/linux-test-project/ltx.git

tools/ltx/Makefile

@@ -0,0 +1,31 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+# Copyright (c) 2023 Cyril Hrubis <chrubis@suse.cz>
+# Copyright (c) 2023 Andrea Cervesato <andrea.cervesato@suse.com>
+#
+# Install script for Linux Test eXecutor
+
+top_srcdir		?= ../..
+
+include $(top_srcdir)/include/mk/env_pre.mk
+
+ifneq ($(wildcard $(abs_srcdir)/ltx-src/*),)
+
+BINARY=ltx
+
+MAKE_TARGETS := $(BINARY)
+
+CFLAGS+=-I$(abs_srcdir)/ltx-src/ -I$(abs_srcdir)/ltx-src/msgpack/
+
+$(BINARY): $(wildcard $(abs_srcdir)/ltx-src/*.c $(abs_srcdir)/ltx-src/msgpack/*.c)
+ifdef VERBOSE
+	$(CC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) $^ $(LDLIBS) -o $@
+else
+	@echo CC $@
+	@$(CC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) $^ $(LDLIBS) -o $@
+endif
+
+INSTALL_DIR := $(prefix)
+
+endif
+
+include $(top_srcdir)/include/mk/generic_leaf_target.mk