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 <[email protected]>
Reviewed-by: Petr Vorel <[email protected]>
Reviewed-by: Cyril Hrubis <[email protected]>
Signed-off-by: Andrea Cervesato <[email protected]>
[ pvorel: Add Subproject commit 7e397fe1a2d34a100c7dbfa452bd5d86ca1ddb77 ]
Signed-off-by: Petr Vorel <[email protected]>

.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 <[email protected]>
+# Copyright (c) 2023 Andrea Cervesato <[email protected]>
+#
+# 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