-msse flag could be handled better by the driver

I bumped into two small issues with -msse and -msse4.2 flags:

1. GHC accepts any flag of the form -msseX.Y, eg. -msse3.14. I think we should validate numbers passed by the user or - even better - pre-define a set of allowed -msse flags. Currently we have this definition:

Flag "msse"         (versionSuffix (\maj min d -> d{ sseVersion = Just (maj, min) }))

1. A direct consequence of above definition is that bash command-line auto-completion does not suggest -msse4.2 flag.

This is somewhat related to Austin's D165

Trac metadata

Trac field	Value
Version	7.9
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Driver
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