Support throwAssertion matcher on Linux

Author: ikesyo

Package.swift

@@ -19,7 +19,7 @@ let package = Package(
                 #if os(macOS)
                 return ["CwlPreconditionTesting", "CwlPosixPreconditionTesting"]
                 #else
-                return []
+                return ["CwlPosixPreconditionTesting"]
                 #endif
             }()
         ),

Sources/Nimble/Matchers/ThrowAssertion.swift

@@ -8,7 +8,7 @@ import CwlPosixPreconditionTesting
 
 public func throwAssertion() -> Predicate<Void> {
     return Predicate { actualExpression in
-    #if arch(x86_64) && canImport(Darwin)
+    #if arch(x86_64)
         let message = ExpectationMessage.expectedTo("throw an assertion")
 
         var actualError: Error?
@@ -45,9 +45,9 @@ public func throwAssertion() -> Predicate<Void> {
             return PredicateResult(bool: caughtException != nil, message: message)
         }
     #else
-        fatalError("The throwAssertion Nimble matcher can only run on x86_64 platforms with " +
-            "Objective-C (e.g. macOS, iPhone 5s or later simulators). You can silence this error " +
-            "by placing the test case inside an #if arch(x86_64) or canImport(Darwin) conditional statement")
+        fatalError("The throwAssertion Nimble matcher can only run on x86_64 platforms." +
+            "You can silence this error " +
+            "by placing the test case inside an #if arch(x86_64) conditional statement")
     #endif
     }
 }

Tests/NimbleTests/Matchers/ThrowAssertionTest.swift

@@ -2,7 +2,7 @@ import Foundation
 import XCTest
 import Nimble
 
-#if canImport(Darwin)
+#if arch(x86_64)
 
 private let error: Error = NSError(domain: "test", code: 0, userInfo: nil)