Update to a new snapshot and migrate to the llvm monorepo.
We now always download everthing so apply all patches (except the ELFv2
patches) unconditionally. Don't imply CLANG fo ELFV2 since the patches
will always apply.
Install llvm-devel.mk for CROSS_TOOLCHAIN support subsuming the
role of xtoolchain-llvm-devel. This means that users will get the
dependency for CROSS_TOOLCHAIN=llvm-devel by installing llvm-devel.
To avoid unnecessicary churn in other xtoolchain-llvm* ports, leave
xtoolchain-llvm-devel in place and make it IGNORE in the -devel case.
Once llvm90 (and maybe llvm80) are updated I'll remove it or move it as
Always install a link from ld.lld to ld as was done by
Sponsored by: DARPA, AFRL