When using meta-clang, it makes sense to use llvm provided by clang
recipe, this ensures that we do not build llvm from oe-core but instead
offer the one from clang recipe

enable rtti and eh for native/nativesdk clang, this is needed for mesa
to build

Let clang PROVIDE llvm

Build AMDGNU and other targets, this is needed for llvm-config to work
properly, since we use llvm-config from clang-native, so its better to
build the targets that are built for clang-native atleast

create version specific symlinks for tblgen anf llvm-config

Signed-off-by: Khem Raj <raj.khem@gmail.com>