The generator name is "Xcode", not "XCode". Fix this typo. Explicitly
exclude the SubDirSpaces test on Xcode because it does not work. Also
tell the RunCMake.File_Generate test when Xcode is not multi-config so
it can exlcude the OutputConflict case.
Inspired-by: Daniele E. Domenichelli <daniele.domenichelli@iit.it>