Import the swift-compiler-crashes test suite.

Add all compiler crash tests to the validation-test/compiler_crashers
subdirectory. Add a RUN: line to each test case according to the current
behavior of the Swift compiler.

Swift SVN r23418

validation-test/compiler_crashers/1898-swift-parser-parsefunctionarguments.swift

@@ -0,0 +1,19 @@
+// RUN: not --crash %swift %s -parse
+
+// Distributed under the terms of the MIT license
+// Test case submitted to project by https://github.com/practicalswift (practicalswift)
+// Test case found by fuzzing
+
+protocol A : a {
+convenience init() {
+class A, "]
+func a<l : NSObject {
+a).f == d>) -> (x(a(v: [(")
+}
+struct c: String {
+}
+let b = c: b {
+func i> {
+var b = e? {
+override func a(B
+}