Update LLVM WoA buildbots for better converage

[omjavaid]

This updates LLVM WoA bots with following changes:

1. Do not run stage1 testing on 2 stage clang bot.
2. Remove redundant workers.
3. Remove -DCOMPILER_RT_BUILD_PROFILE=OFF
4. Add compiler-rt to single stage bot
5. Set clean=False for the 2stage bots
6. Set "-DCLANG_DEFAULT_LINKER=lld" for all WoA bots