tests/tcg: Replace /bin/true by true (required on macOS)

/bin/true is missing on macOS, but simply "true" is available as a shell builtin.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20210128135627.2067003-1-sw@weilnetz.de>
Message-Id: <20210202134001.25738-12-alex.bennee@linaro.org>

tests/tcg/Makefile.qemu

@@ -90,11 +90,11 @@ run-guest-tests: guest-tests
 
 else
 guest-tests:
-	$(call quiet-command, /bin/true, "BUILD", \
+	$(call quiet-command, true, "BUILD", \
 		"$(TARGET) guest-tests SKIPPED")
 
 run-guest-tests:
-	$(call quiet-command, /bin/true, "RUN", \
+	$(call quiet-command, true, "RUN", \
 		"tests for $(TARGET) SKIPPED")
 endif