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/0275-swift-parser-parseexprpostfix.swift

@@ -0,0 +1,16 @@
+// 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
+
+struct q<q : n, p: n where p.q == q.q> {
+}
+o q: n =  { m, i j
+}(q, n> {
+l {
+    typealias f
+    k m p<i) {
+     m
+    }
+}