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/1859-swift-constraints-solution-solution.swift

@@ -0,0 +1,16 @@
+// RUN: not %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
+
+0
+class A<B {
+let x {
+extension Array {
+}
+class b(Any, e = a
+func compose<T) -> {
+}
+class A {
+let start = b())