treat byte order mark as zero-width whitespace

The U+FEFF ZERO WIDTH NO-BREAK SPACE Unicode character, better known as BYTE ORDER MARK (BOM), currently gives a lexical error:

$ printf '\xEF\xBB\xBF\nz = "str"\n' > z.hs
$ ghci z.hs
GHCi, version 6.8.0.20070927: http://www.haskell.org/ghc/  :? for help
Loading package base ... linking ... done.

z.hs:1:0: lexical error at character '\65279'
Failed, modules loaded: none.
Prelude> Leaving GHCi.

The character is only in categories Other and Format, not Space, but I think we should lex it as whitespace anyway (with zero width for the purposes of the layout rule). Ideally Haskell' would do likewise.

Trac metadata

Trac field	Value
Version	6.8
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Parser)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown
Architecture	Unknown