Enable SQLITE_ENABLE_SNAPSHOT in the GRDBSQLite trait, on Darwin platforms

Author: groue

Package.swift

@@ -4,8 +4,18 @@
 import Foundation
 import PackageDescription
 
+let darwinPlatforms: [Self] = [
+    .iOS,
+    .macOS,
+    .macCatalyst,
+    .tvOS,
+    .visionOS,
+    .watchOS,
+]
 var swiftSettings: [SwiftSetting] = [
     .define("SQLITE_ENABLE_FTS5"),
+    // SQLite snapshots are available on the system SQLite on Darwin platforms.
+    .define("SQLITE_ENABLE_SNAPSHOT", .when(platforms: darwinPlatforms, traits: ["GRDBSQLite"])
 ]
 var cSettings: [CSetting] = []
 var dependencies: [PackageDescription.Package.Dependency] = []