Separate stdout and stderr in tests

POSIX leaves undefined the order of output if stderr is injected into stdout,
and in practice it differs on Windows (Linux buffers both streams separately,
Windows interleaves them as they arrive without buffering).
This should help testing on other platforms

test/asm/test.sh

@@ -3,15 +3,17 @@ export LC_ALL=C
 
 o=$(mktemp)
 gb=$(mktemp)
-before=$(mktemp)
-after=$(mktemp)
+input=$(mktemp)
+output=$(mktemp)
+errput=$(mktemp)
 rc=0
 
 for i in *.asm; do
 	for variant in '' '.pipe'; do
 		if [ -z "$variant" ]; then
-			../../rgbasm -Weverything -o $o $i > $after 2>&1
+			../../rgbasm -Weverything -o $o $i > $output 2> $errput
 			desired_output=${i%.asm}.out
+			desired_errput=${i%.asm}.err
 		else
 			# `include-recursion.asm` refers to its own name inside the test code.
 			# Skip testing with stdin input for that file.
@@ -23,27 +25,34 @@ for i in *.asm; do
 			# stdin redirection makes the input an unseekable pipe - a scenario
 			# that's harder to deal with and was broken when the feature was
 			# first implemented.
-			cat $i | ../../rgbasm -Weverything -o $o - > $after 2>&1
+			cat $i | ../../rgbasm -Weverything -o $o - > $output 2> $errput
 
+			# Use two otherwise unused files for temp storage
+			desired_output=$input
+			desired_errput=$gb
 			# Escape regex metacharacters
-			desired_output=$before
 			subst="$(printf '%s\n' "$i" | sed 's:[][\/.^$*]:\\&:g')"
+			# Replace the file name with a dash to match changed output
 			sed "s/$subst/-/g" ${i%.asm}.out > $desired_output
+			sed "s/$subst/-/g" ${i%.asm}.err > $desired_errput
 		fi
 
-		diff -u $desired_output $after
+		diff -u $desired_output $output
 		rc=$(($? || $rc))
+		diff -u $desired_errput $errput
+		rc=$(($? || $rc))
+
 		bin=${i%.asm}.out.bin
 		if [ -f $bin ]; then
-			../../rgblink -o $gb $o > $after 2>&1
-			dd if=$gb count=1 bs=$(printf %s $(wc -c < $bin)) > $after 2>/dev/null
-			hexdump -C $after > $before && mv $before $after
-			hexdump -C $bin > $before
-			diff -u $before $after
+			../../rgblink -o $gb $o > $output 2>&1
+			dd if=$gb count=1 bs=$(printf %s $(wc -c < $bin)) > $output 2>/dev/null
+			hexdump -C $output > $input && mv $input $output
+			hexdump -C $bin > $input
+			diff -u $input $output
 			rc=$(($? || $rc))
 		fi
 	done
 done
 
-rm -f $o $gb $before $after
+rm -f $o $gb $input $output
 exit $rc