Add LinuxMain for tests w/ Swift <5.4

Author: Frizlab

Tests/LinuxMain.swift

@@ -0,0 +1,14 @@
+import XCTest
+
+@testable import SignalHandlingTests
+
+var tests: [XCTestCaseEntry] = [
+	testCase([
+		("testNSConditionLock", NSConditionLockTest.testNSConditionLock),
+	]),
+	testCase([
+		("testBasicSignalDelayByUnsigaction", SignalHandlingTests.testBasicSignalDelayByUnsigaction),
+		("testBasicSignalDelayByBlock", SignalHandlingTests.testBasicSignalDelayByBlock),
+	]),
+]
+XCTMain(tests)