Remove ${} from CMAKE_SYSTEM variable in IF statement
Remove ${} from CMAKE_SYSTEM variable in IF statement

IF statement interprets a variable without ${}.

And without this, CMAKE_SYSTEM is not checked correctly on CMAKE 3.4.1.

Signed-off-by: derselbst <b889781553847ce3841df1a0830d2b8e9fe72fca@googlemail.com>

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