[Docs] [Support] System Library to Support Library transition along with minor...

[Docs] [Support] System Library to Support Library transition along with minor corrections to reflect it.

System Library has been a long deprecated term along with the path lib/System, having been superseded/renamed
to the Support Library a long time ago. These patches reflect those changes in documentation as well as
update some outdated examples and provide context to the origin of the Support Library.

Differential Revision: https://reviews.llvm.org/D52107

llvm-svn: 342500