Fix SECTION UNION alignment depending on piece order

test/link/test.sh

@@ -390,6 +390,15 @@ rgblinkQuiet "$otemp" "$gbtemp" 2>"$outtemp"
 tryDiff "$test"/out.err "$outtemp"
 evaluateTest
 
+test="section-union/compat"
+startTest
+"$RGBASM" -o "$otemp" "$test"/a.asm
+"$RGBASM" -o "$gbtemp2" "$test"/b.asm
+continueTest
+rgblinkQuiet -o "$gbtemp" -l "$test"/script.link "$otemp" "$gbtemp2"
+tryCmpRom "$test"/ref.out.bin
+evaluateTest
+
 test="section-union/good"
 startTest
 "$RGBASM" -o "$otemp" "$test"/a.asm