tests/tcg: don't silently skip the gdb tests

Otherwise people won't know what they are missing.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20210202134001.25738-10-alex.bennee@linaro.org>

tests/tcg/multiarch/Makefile.target

@@ -63,8 +63,11 @@ run-gdbstub-qxfer-auxv-read: sha1
 		--bin $< --test $(MULTIARCH_SRC)/gdbstub/test-qxfer-auxv-read.py, \
 	"basic gdbstub qXfer:auxv:read support")
 
-EXTRA_RUNS += run-gdbstub-sha1 run-gdbstub-qxfer-auxv-read
+else
+run-gdbstub-%:
+	$(call skip-test, "gdbstub test $*", "need working gdb")
 endif
+EXTRA_RUNS += run-gdbstub-sha1 run-gdbstub-qxfer-auxv-read
 
 
 # Update TESTS