[Build][Concurrency] Fix Concurrency build to work for Linux.

`SWIFT_BUILD_STATIC_STDLIB` is not mutually exclusive with
`SWIFT_BUILD_DYNAMIC_STDLIB`, and Linux sets both, so we can't use
`SWIFT_BUILD_STATIC_STDLIB` to conditionalise things.

The linker error about duplicate definitions for the threading error
handler was happening because we were forced to include the object
containing that symbol; moving it to another object should fix that.

And it turns out there's a way to get CMake to include the threading
object library only when building a shared object, so use that too.

rdar://90776105

Author: al45tair

stdlib/public/Concurrency/CMakeLists.txt

@@ -30,10 +30,7 @@ if(CMAKE_SYSTEM_NAME STREQUAL Windows)
   list(APPEND swift_concurrency_private_link_libraries Synchronization)
 endif()
 
-set(swift_concurrency_incorporate_object_libraries)
-if(NOT SWIFT_BUILD_STATIC_STDLIB)
-  list(APPEND swift_concurrency_incorporate_object_libraries swiftThreading)
-endif()
+set(swift_concurrency_incorporate_object_libraries_so swiftThreading)
 
 if("${SWIFT_CONCURRENCY_GLOBAL_EXECUTOR}" STREQUAL "dispatch")
   if(NOT CMAKE_SYSTEM_NAME STREQUAL Darwin)
@@ -77,11 +74,6 @@ endif()
 list(APPEND SWIFT_RUNTIME_CONCURRENCY_C_FLAGS
   "-D__STDC_WANT_LIB_EXT1__=1")
 
-if(SWIFT_BUILD_STATIC_STDLIB)
-  list(APPEND SWIFT_RUNTIME_CONCURRENCY_C_FLAGS
-    "-DSWIFT_BUILD_STATIC_STDLIB=1")
-endif()
-
 add_swift_target_library(swift_Concurrency ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES} IS_STDLIB
   ../CompatibilityOverride/CompatibilityOverride.cpp
   Actor.cpp
@@ -125,6 +117,7 @@ add_swift_target_library(swift_Concurrency ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES} I
   TaskLocal.swift
   TaskSleep.swift
   ThreadSanitizer.cpp
+  ThreadingError.cpp
   TracingSignpost.cpp
   AsyncStreamBuffer.swift
   AsyncStream.swift
@@ -142,7 +135,8 @@ add_swift_target_library(swift_Concurrency ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES} I
   SWIFT_MODULE_DEPENDS_WINDOWS CRT
 
   PRIVATE_LINK_LIBRARIES ${swift_concurrency_private_link_libraries}
-  INCORPORATE_OBJECT_LIBRARIES ${swift_concurrency_incorporate_object_libraries}
+  INCORPORATE_OBJECT_LIBRARIES_SHARED_ONLY
+    ${swift_concurrency_incorporate_object_libraries_so}
   LINK_LIBRARIES ${swift_concurrency_link_libraries}
 
   C_COMPILE_FLAGS

stdlib/public/Concurrency/Error.cpp

@@ -34,15 +34,3 @@ void swift::swift_Concurrency_fatalError(uint32_t flags, const char *format,
   va_start(val, format);
   swift_Concurrency_fatalErrorv(flags, format, val);
 }
-
-#if !SWIFT_BUILD_STATIC_STDLIB
-// Handle fatal errors from the threading library
-SWIFT_ATTRIBUTE_NORETURN
-SWIFT_FORMAT(1, 2)
-void swift::threading::fatal(const char *format, ...) {
-  va_list val;
-
-  va_start(val, format);
-  swift_Concurrency_fatalErrorv(0, format, val);
-}
-#endif // !SWIFT_BUILD_STATIC_STDLIB

stdlib/public/Concurrency/ThreadingError.cpp

@@ -0,0 +1,26 @@
+//===--- ThreadingError.cpp - Error handling support code -----------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2017 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "swift/Threading/Errors.h"
+#include <cstdio>
+
+#include "Error.h"
+
+// Handle fatal errors from the threading library
+SWIFT_ATTRIBUTE_NORETURN
+SWIFT_FORMAT(1, 2)
+void swift::threading::fatal(const char *format, ...) {
+  va_list val;
+
+  va_start(val, format);
+  swift_Concurrency_fatalErrorv(0, format, val);
+}