Merge pull request #1277 from practicalswift/swiftc-28252-swift-constraints-constraintsystem-assignfixedtype

[swiftc] Add test case for crash triggered in swift::constraints::ConstraintSystem::assignFixedType(…)

Author: gribozavr

validation-test/compiler_crashers/28252-swift-constraints-constraintsystem-assignfixedtype.swift

@@ -0,0 +1,8 @@
+// RUN: not --crash %target-swift-frontend %s -parse
+// REQUIRES: asserts
+
+// Distributed under the terms of the MIT license
+// Test case submitted to project by https://github.com/practicalswift (practicalswift)
+// Test case found by fuzzing
+
+{println(""""?struct{