[build] Add a Swift Package manifest

This will allow using the project as a dependency of other Swift Packages.

Author: egorzhdan

Package.swift

@@ -0,0 +1,47 @@
+// swift-tools-version:5.9
+// WARNING: Swift Package Manager support is experimental, please consider using CMake to build this project.
+
+import PackageDescription
+import class Foundation.ProcessInfo
+
+let env = ProcessInfo.processInfo.environment
+
+guard let llvmHeaderPath = env["SWIFT_LLVM_BINDINGS_PATH_TO_LLVM_HEADERS"] else {
+  fatalError("please pass an environment variable to swift-package: " +
+               "SWIFT_LLVM_BINDINGS_PATH_TO_LLVM_HEADERS " +
+               "(e.g. swift/llvm-project/llvm/include)")
+}
+let llvmModuleMapPath = "\(llvmHeaderPath)/llvm/module.modulemap"
+guard let llvmGeneratedHeaderPath = env["SWIFT_LLVM_BINDINGS_PATH_TO_LLVM_GENERATED_HEADERS"] else {
+  fatalError("please pass an environment variable to swift-package: " +
+               "SWIFT_LLVM_BINDINGS_PATH_TO_LLVM_GENERATED_HEADERS " +
+               "(e.g. swift/build/Ninja-DebugAssert/llvm-macosx-arm64/include)")
+}
+
+let llvmSwiftSettings: [SwiftSetting] = [
+  .interoperabilityMode(.Cxx),
+  .unsafeFlags([
+                 "-I\(llvmHeaderPath)",
+                 "-Xcc", "-I\(llvmHeaderPath)",
+                 "-I\(llvmGeneratedHeaderPath)",
+                 "-Xcc", "-I\(llvmGeneratedHeaderPath)",
+                 "-Xcc", "-fmodule-map-file=\(llvmModuleMapPath)",
+               ]),
+]
+
+let package = Package(
+  name: "SwiftLLVMBindings",
+  products: [
+    .library(name: "SwiftLLVM_Utils", targets: ["SwiftLLVM_Utils"]),
+  ],
+  targets: [
+    .target(
+      name: "SwiftLLVM_Utils",
+      path: "Sources/LLVM",
+      exclude: ["CMakeLists.txt"],
+      sources: ["LLVM_Utils.swift"],
+      swiftSettings: llvmSwiftSettings
+    ),
+  ],
+  cxxLanguageStandard: .cxx17
+)