llvm-native: default clang to the HOST triple, not Redox

LLVM_DEFAULT_TARGET_TRIPLE was ${TARGET} (redox), so the host clang defaulted
to x86_64-unknown-redox and searched the Redox sysroot for the C++ stdlib when
libclc compiled its host prepare_builtins.cpp -> 'type_traits' file not found.
A host clang must default to the host triple (the redoxer toolchain's clang
does exactly this: Target x86_64-unknown-linux-gnu). Set it to
${COOKBOOK_HOST_TARGET}. libclc's .cl->bitcode compiles pass -target amdgcn
explicitly, so the host default does not affect them.

local/recipes/dev/llvm-native/recipe.toml

@@ -70,7 +70,7 @@ COOKBOOK_SOURCE="$COOKBOOK_SOURCE/llvm"
     -DLLVM_BUILD_TESTS=Off \
     -DLLVM_INCLUDE_EXAMPLES=Off \
     -DLLVM_INCLUDE_TESTS=Off \
-    -DLLVM_DEFAULT_TARGET_TRIPLE="${TARGET}" \
+    -DLLVM_DEFAULT_TARGET_TRIPLE="${COOKBOOK_HOST_TARGET}" \
     -DLLVM_ENABLE_LTO=Off \
     -DLLVM_ENABLE_RTTI=On \
     -DLLVM_ENABLE_THREADS=On \