Do not try to build socket_scm_helper if not softmmu target
is available. This fixes:

  $ make check-block
  Generating qemu-version.h with a meson_exe.py custom command
  make: *** No rule to make target 'tests/qemu-iotests/socket_scm_helper', needed by 'check-block'.  Stop.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 tests/Makefile.include | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tests/Makefile.include b/tests/Makefile.include
index 40d909badc..d257777560 100644
--- a/tests/Makefile.include
+++ b/tests/Makefile.include
@@ -136,7 +136,9 @@ check-acceptance: check-venv $(TESTS_RESULTS_DIR) get-vm-images
 check:
 
 ifeq ($(CONFIG_TOOLS)$(CONFIG_POSIX),yy)
+ifneq ($(TARGET_DIRS),)
 QEMU_IOTESTS_HELPERS-$(CONFIG_LINUX) = tests/qemu-iotests/socket_scm_helper$(EXESUF)
+endif
 check: check-block
 check-block: $(SRC_PATH)/tests/check-block.sh qemu-img$(EXESUF) \
 		qemu-io$(EXESUF) qemu-nbd$(EXESUF) $(QEMU_IOTESTS_HELPERS-y) \
-- 
2.26.2