Genex: Fix indentation in docs.
cmSystemTools: Fix typo in comment.
De-duplicate version comparison code.

Extend the VersionCompare in cmSystemTools to handle 8 components,
and port the if command to use that.
Add generator expressions for version comparision.
Add generator expressions for compiler versions.

New generator expressions allow retrieval of the version per language,
as well as equality comparison.
Style: Don't put an else after a return.
Merge topic 'minor-cleanup' into next

e3b7eac Style: Don't put an else after a return.
ad304a2 cmSystemTools: Fix typo in comment.
08319e0 Genex: Fix indentation in docs.
Merge topic 'version-compare-genex' into next

2d5c845 Add generator expressions for compiler versions.
1d0818d Add generator expressions for version comparision.
d366604 De-duplicate version comparison code.