Update to a new snapshot and add FLANG and MLIR options
Add two new options:
- FLANG (Fortran 2018 compiler)
- MLIR (Multi-Level Intermediate Representation support)
MLIR is enabled by default and required by FLANG. FLANG is not yet
enabled by default because it is broken with LLVM_LINK_LLVM_DYLIB=ON
which results in a truly enormous package (500+MB .txz).
Sponsored by: DARPA