[Runtime] Expose accessible function lookup as stdlib SPI

`findAccessibleFunction` has to be accessible from Concurrency
and Distributed modules to be able to lookup distributed accessors.

Author: xedin

include/swift/Runtime/AccessibleFunction.h

@@ -0,0 +1,34 @@
+//===---- AcceesibleFunction.h - Runtime accessible functions ---*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2021 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+//
+// The runtime interface for functions accessible by name.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_RUNTIME_ACCESSIBLE_FUNCTION_H
+#define SWIFT_RUNTIME_ACCESSIBLE_FUNCTION_H
+
+#include "swift/ABI/Metadata.h"
+
+#include <cstdint>
+
+namespace swift {
+namespace runtime {
+
+SWIFT_RUNTIME_STDLIB_SPI const AccessibleFunctionRecord *
+swift_findAccessibleFunction(const char *targetNameStart,
+                             size_t targetNameLength);
+
+} // end namespace runtime
+} // end namespace swift
+
+#endif

stdlib/public/runtime/AccessibleFunction.cpp

@@ -18,9 +18,9 @@
 #include "Private.h"
 #include "swift/Basic/Lazy.h"
 #include "swift/Demangling/Demangler.h"
+#include "swift/Runtime/AccessibleFunction.h"
 #include "swift/Runtime/Concurrent.h"
 #include "swift/Runtime/Metadata.h"
-#include "Private.h"
 
 #include <cstdint>
 
@@ -127,10 +127,14 @@ _searchForFunctionRecord(AccessibleFunctionsState &S, llvm::StringRef name) {
   return nullptr;
 }
 
-static const AccessibleFunctionRecord *
-_findAccessibleFunction(llvm::StringRef name) {
+SWIFT_RUNTIME_STDLIB_SPI
+const AccessibleFunctionRecord *
+swift::runtime::swift_findAccessibleFunction(const char *targetNameStart,
+                                             size_t targetNameLength) {
   auto &S = Functions.get();
 
+  llvm::StringRef name{targetNameStart, targetNameLength};
+
   // Look for an existing entry.
   {
     auto snapshot = S.Cache.snapshot();