Fix the failure of hard_coded/runtime_opt on Windows.

tests/hard_coded/runtime_opt.exp2:
    Alternative expected output for where stdout and stderr are
    interleaved differently.

tests/hard_coded/runtime_opt.m:
    Document what the expected outputs are for.

tests/hard_coded/runtime_opt.exp2

@@ -0,0 +1,15 @@
+Option `--nondetstack-size-kwords=256 --small-nondetstack-size-kwords=256':
+Hello world (with non-standard options).
+
+Option `--nondet-stack-size-kwords=256 --small-nondet-stack-size-kwords=256':
+Hello world (with non-standard options).
+
+Option `--detstack-size=128 --small-detstack-size=128':
+Hello world (with non-standard options).
+
+Option `--this-is-not-a-real-option':
+The MERCURY_OPTIONS environment variable contains an invalid option.
+Please refer to the Environment Variables section of the Mercury
+User's Guide for details.
+mercury_runtime: unrecognized option: `this-is-not-a-real-option'
+

tests/hard_coded/runtime_opt.m

@@ -1,6 +1,9 @@
 %---------------------------------------------------------------------------%
 % vim: ts=4 sw=4 et ft=mercury
 %---------------------------------------------------------------------------%
+% The different exepcted outputs correspond to different interleavings of
+% standard output and error.
+%---------------------------------------------------------------------------%
 
 :- module runtime_opt.
 :- interface.