Add a build preset to build a minimal toolchain without a host Swift compiler

Create a new build present that builds without a host Swift compiler, which
is meant to be sufficient to bootstrap a full Swift toolchain on a
new host.

Author: DougGregor

utils/build-presets.ini

@@ -890,6 +890,30 @@ installable-package=%(installable_package)s
 # in Linux CI bots
 relocate-xdg-cache-home-under-build-subdir
 
+[preset: minimal_toolchain_without_host_swift]
+swift-install-components=autolink-driver;compiler;clang-resource-dir-symlink;libexec;stdlib;sdk-overlay;toolchain-tools;license
+llvm-install-components=llvm-ar;llvm-ranlib;llvm-cov;llvm-profdata;IndexStore;clang;clang-resource-headers;compiler-rt;clangd;lld;LTO;clang-features-file
+
+release
+minimal-cxx-bootstrap
+
+llbuild
+swiftpm
+swift-driver
+
+build-ninja
+install-llvm
+install-swift
+install-llbuild
+install-swiftpm
+install-swift-driver
+install-prefix=/usr
+install-destdir=%(install_destdir)s
+relocate-xdg-cache-home-under-build-subdir
+
+skip-build-benchmarks
+skip-early-swift-driver
+skip-build-lldb
 
 [preset: buildbot_linux_base]
 mixin-preset=