Remove the restriction that target intrinsics can only involve legal types. ...

Remove the restriction that target intrinsics can only involve legal types.  Targets can perfects well support intrinsics on illegal types, as long as they are prepared to perform custom expansion during type legalization.  For example, a target where i64 is illegal might still support the i64 intrinsic operation using pairs of i32's.  ARM already does some expansions like this for non-intrinsic operations.

llvm-svn: 147472