Merge pull request #712 from practicalswift/sourcekit-055-swift-valuedecl-getoverloadsignature

[SourceKit] Add test case for crash triggered in swift::ValueDecl::getOverloadSignature()

Author: gribozavr

validation-test/IDE/crashers/055-swift-valuedecl-getoverloadsignature.swift

@@ -0,0 +1,6 @@
+// RUN: not --crash %target-swift-ide-test -code-completion -code-completion-token=A -source-filename=%s
+let a{
+protocol A{
+extension{
+struct B{func i(Void
+func#^A^#