LLVM 9.0.0

[jcsiadal]

Upgrade LLVM compiler to 9.0.0. Reference to #767 opened on Jun 28, #2018.

In my initial work on OpenSUSE 15.1, I wasn't able to get the current llvm6 package to build correctly. My initial tests with llvm9 have been much more positive.

I think there are three items which will need to be addressed:

1. Do we build flang, move to f18 (flang's soon-to-be replacement), or build both?
2. If we build both, should the C and Fortran compiler components be split into different RPMs, so the user can select their Fortran compiler?
3. Should we implement enhancement issue Splitting up llvm as a compiler and llvm as a library #574 : splitting up llvm as a compiler and llvm as a library?

[jcsiadal]

A couple of more notes on this:

• The latest release of flang is based on LLVM7. It won't build against 8 or 9. A recent flang commit may work, but I haven't looked into it.
• f18 is validated against LLVM7 and 8. I would expect support for LLVM9 soon.

I can take the assignment to package this, but this will need a TSC decision on which version to use. The obvious implementation is to build two versions: LLVM9 (adding f18 as soon as available) and LLVM7/flang using the March 2019 release.

[jcsiadal]

Closed with PR #1087 merge.