[Backtracing] Add some more tests.

Add tests for the new immediate on-crash message and the backtrace timing
message.

rdar://118055527

test/Backtracing/EarlyMessage.swift

@@ -0,0 +1,45 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift %s -parse-as-library -Onone -g -o %t/EarlyMessage
+// RUN: (env SWIFT_BACKTRACE=enable=yes,cache=no %target-run %t/EarlyMessage 2>&1 || true) | %FileCheck %s
+
+// UNSUPPORTED: use_os_stdlib
+// UNSUPPORTED: back_deployment_runtime
+// UNSUPPORTED: asan
+// REQUIRES: executable_test
+// REQUIRES: backtracing
+// REQUIRES: OS=macosx || OS=linux-gnu
+
+func level1() {
+  level2()
+}
+
+func level2() {
+  level3()
+}
+
+func level3() {
+  level4()
+}
+
+func level4() {
+  level5()
+}
+
+func level5() {
+  print("About to crash")
+  let ptr = UnsafeMutablePointer<Int>(bitPattern: 4)!
+  ptr.pointee = 42
+}
+
+@main
+struct EarlyMessage {
+  static func main() {
+    level1()
+  }
+}
+
+// Make sure we get the early crash message from the backtracer (the first
+// part is generated by the runtime itself; the "done ***" on the end is from
+// swift-backtrace).
+
+// CHECK: *** Signal {{[0-9]+}}: Backtracing from 0x{{[0-9a-f]+}}... done ***

test/Backtracing/Timing.swift

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+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift %s -parse-as-library -Onone -g -o %t/Timing
+// RUN: (env SWIFT_BACKTRACE=enable=yes,cache=no %target-run %t/Timing 2>&1 || true) | %FileCheck %s
+
+// UNSUPPORTED: use_os_stdlib
+// UNSUPPORTED: back_deployment_runtime
+// UNSUPPORTED: asan
+// REQUIRES: executable_test
+// REQUIRES: backtracing
+// REQUIRES: OS=macosx || OS=linux-gnu
+
+func level1() {
+  level2()
+}
+
+func level2() {
+  level3()
+}
+
+func level3() {
+  level4()
+}
+
+func level4() {
+  level5()
+}
+
+func level5() {
+  print("About to crash")
+  let ptr = UnsafeMutablePointer<Int>(bitPattern: 4)!
+  ptr.pointee = 42
+}
+
+@main
+struct Timing {
+  static func main() {
+    level1()
+  }
+}
+
+// The backtracer should say how long the backtrace took, in seconds, with
+// two decimal places.
+
+// CHECK: Backtrace took {{[0-9]+}}.{{[0-9][0-9]}}s