[MLton] commit r4349: preliminary support for compiler specific annotations

[Matthew Fluet]

Added very simple support for compiler specific annotations.  If an
annotation contains ":", then the text preceding the ":" is meant to
denote a compiler.  For MLton, if the text preceding the ":" is equal
to "mlton", then the remaining annotation is scanned as a normal
annotation.  If the text preceding the ":" is not-equal to "mlton",
then the annotation is ignored, and no warning is issued.


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U   mlton/trunk/mlton/control/control-flags.sig
U   mlton/trunk/mlton/control/control-flags.sml
U   mlton/trunk/mlton/elaborate/elaborate-mlbs.fun
U   mlton/trunk/mlton/main/main.fun