[m-rev.] for review: reporting stats NOT to stderr

[Zoltan Somogyi]

We need the capability to print stats to a user-selected stream,
and not just to stderr, if we are to convert the rest of the compiler
to always use explicit streams.

This diff makes the change only for the C backend. Would anyone
volunteer to make the change to for the C# and Java backends?

For review by anyone. Note that this diff is from before replacing
any ML_ prefixes with MR_ prefixes on code moved from the library
to the runtime, to reduce clutter in any manual diffs.

Zoltan.
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