Add a (now fixed) compiler crash test case contributed by Jasl on the swift-dev mailing list

Author: gribozavr

validation-test/compiler_crashers_2_fixed/0037-SILWitnessVisitor.swift

@@ -0,0 +1,11 @@
+// RUN: not %target-swift-frontend %s -emit-silgen
+
+protocol FooType {
+  func bar(b: Int)
+}
+
+extension FooType {
+  func bar(a: Int, b: Int) {}
+}
+
+struct Foo : FooType {}