Don't compile symbols for Linux that are not yet available (#22)

Author: davdroman

Sources/CustomDump/Conformances/Foundation.swift

@@ -5,7 +5,8 @@ import Foundation
 #endif
 
 // NB: Xcode 13 does not include macOS 12 SDK
-#if compiler(>=5.5) && !os(macOS) && !targetEnvironment(macCatalyst)
+// NB: Swift 5.5 does not include AttributedString in Linux (yet)
+#if compiler(>=5.5) && !os(macOS) && !targetEnvironment(macCatalyst) && !os(Linux)
   @available(iOS 15, macOS 12, tvOS 15, watchOS 8, *)
   extension AttributedString: CustomDumpRepresentable {
     public var customDumpValue: Any {

Tests/CustomDumpTests/DumpTests.swift

@@ -724,7 +724,7 @@ final class DumpTests: XCTestCase {
   func testFoundation() {
     var dump = ""
 
-    #if compiler(>=5.5) && !os(macOS)
+    #if compiler(>=5.5) && !os(macOS) && !os(Linux)
       if #available(iOS 15, macOS 12, tvOS 15, watchOS 8, *) {
         dump = ""
         customDump(