[build] Build host toolchain with thread enabled

`buildbot_linux` builds more host tools and some of them including
SwiftPM cannot work without thread on host.

Author: kateinoigakukun

utils/build-presets.ini

@@ -1275,10 +1275,6 @@ sourcekit-lsp=0
 [preset: buildbot_incremental_linux_crosscompile_wasm]
 mixin-preset=buildbot_linux
 llvm-targets-to-build=X86;ARM;AArch64;WebAssembly
-# Ensure single-thread-mode is not broken because it's used
-# by stdlib for wasm32 in SwiftWasm fork.
-swift-stdlib-single-threaded-concurrency=1
-swift-threading-package=none
 
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 # OS X Package Builders