test: Ignore failures to remove the output file in some cases

When running tests with busybox as shell, removing the output
log file for the stacksmash-asan testcase fails like this
occasionally:

    rm: can't remove 'log1-stacksmash-asan': Permission denied

This only seems to happen with the i686 build of busybox.

Avoid breaking builds by simply making it ignore errors from this
particular "rm" command.

Author: mstorsjo

test/Makefile

@@ -351,7 +351,7 @@ $(FAILURE_TEST_TARGETS): .failtested.%$(EXEEXT): %$(EXEEXT) .copied.%$(EXEEXT) $
 			exit 1; \
 			;; \
 		esac; \
-		rm -f $$OUT; \
+		rm -f $$OUT || true; \
 	fi
 	@touch $@