llvm90:
Enable OpenMP on power64. [0]

Add an option to link ld.lld to ld and enable by default on power64. [1]

xtoolchain-llvm-devel:
Add the ability to disable linking ld.lld to ld in slave ports.

xtoolchain-llvm90:
Disable linking ld.lld to ld since llvm90 can now do it.

PR: 240516 [0]
Submitted by: pkubaj [0]
Requested by: kib [1]