build: add an initial CMake based build system for DocC

Using this (along with its dependencies) allows us to significantly
reduce the build times for the Swift toolchain (~7% of the overall build
time in local testing).

CMakeLists.txt

@@ -0,0 +1,31 @@
+#[[
+This source file is part of the swift-format open source project
+
+Copyright (c) 2024 Apple Inc. and the DocC project authors
+Licensed under Apache License v2.0 with Runtime Library Exception
+
+See https://swift.org/LICENSE.txt for license information
+#]]
+
+cmake_minimum_required(VERSION 3.24)
+
+project(docc
+  LANGUAGES Swift)
+
+set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
+set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
+set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
+
+set(CMAKE_Swift_MODULE_DIRECTORY ${CMAKE_BINARY_DIR}/swift)
+set(CMAKE_Swift_COMPILE_OPTIONS_MSVC_RUNTIME_LIBRARY MultiThreadedDLL)
+
+include(GNUInstallDirs)
+
+find_package(ArgumentParser CONFIG)
+find_package(SwiftCrypto CONFIG)
+find_package(SwiftMarkdown CONFIG)
+find_package(LMDB CONFIG)
+find_package(SymbolKit CONFIG)
+find_package(cmark-gfm CONFIG)
+
+add_subdirectory(Sources)

Sources/CMakeLists.txt

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+#[[
+This source file is part of the swift-format open source project
+
+Copyright (c) 2024 Apple Inc. and the DocC project authors
+Licensed under Apache License v2.0 with Runtime Library Exception
+
+See https://swift.org/LICENSE.txt for license information
+#]]
+
+add_subdirectory(SwiftDocC)
+add_subdirectory(SwiftDocCUtilities)
+add_subdirectory(docc)
+