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/1038-swift-constraints-constraintsystem-simplifyconstraint.swift

@@ -0,0 +1,20 @@
+// 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
+
+assert() {
+var e: A {
+}
+map()] = Swift.a<T) {
+typealias d() {
+struct c == D>Bool) -> {
+}
+}
+}
+}()
+protocol c : d {
+let f = 0) {
+self] = "",")
+typealias d