Update backdeploy test to handle 5.6 compat lib

This patch updates the concurrency backdeployment test to handle the
inclusion of the Swift 5.6 compatibility library.

macOS12 will have the 5.6 library applied to it, so the
_swift_FORCE_LOAD_$_swiftCompatibility56 symbol is defined weakly.

Author: etcwilde

test/Concurrency/Backdeploy/weak_linking.swift

@@ -1,19 +1,30 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-frontend %s -target %target-cpu-apple-macosx12.0 -module-name main -emit-ir -o %t/new.ir
+
+// RUN: %target-swift-frontend %s -target %target-cpu-apple-macosx13.0 -module-name main -emit-ir -o %t/new.ir
 // RUN: %FileCheck %s --check-prefix=NEW < %t/new.ir
-// RUN: %target-swift-frontend %s -target %target-cpu-apple-macosx10.15 -module-name main -emit-ir -o %t/old.ir -disable-availability-checking
-// RUN: %FileCheck %s --check-prefix=OLD < %t/old.ir
+
+// RUN: %target-swift-frontend %s -target %target-cpu-apple-macosx12.0 -module-name main -emit-ir -o %t/backdeploy_56.ir
+// RUN: %FileCheck %s --check-prefix=BACKDEPLOY56 < %t/backdeploy_56.ir
+
+// RUN: %target-swift-frontend %s -target %target-cpu-apple-macosx10.15 -module-name main -emit-ir -o %t/backdeployed_concurrency.ir -disable-availability-checking
+// RUN: %FileCheck %s --check-prefixes=BACKDEPLOY_CONCURRENCY,BACKDEPLOY56 < %t/backdeployed_concurrency.ir
+
 // RUN: %target-swift-frontend %s -target %target-cpu-apple-macosx10.15 -O -module-name main -emit-ir -o %t/optimized.ir -disable-availability-checking
 // RUN: %FileCheck %s --check-prefix=OPTIMIZED < %t/optimized.ir
 
 
 // REQUIRES: OS=macosx
 
 // NEW-NOT: extern_weak
-// OLD: @"$sScPMn" = extern_weak global
-// OLD: declare extern_weak swiftcc i8* @swift_task_alloc
-// OLD: declare extern_weak swiftcc %swift.metadata_response @"$sScPMa"
-// OLD: declare extern_weak swiftcc i8 @"$sScP8rawValues5UInt8Vvg"
+
+// BACKDEPLOY_CONCURRENCY: @"$sScPMn" = extern_weak global
+// BACKDEPLOY_CONCURRENCY: declare extern_weak swiftcc i8* @swift_task_alloc
+// BACKDEPLOY_CONCURRENCY: declare extern_weak swiftcc %swift.metadata_response @"$sScPMa"
+
+// BACKDEPLOY_CONCURRENCY: declare extern_weak void @"_swift_FORCE_LOAD_$_swiftCompatibilityConcurrency"()
+// BACKDEPLOY56: declare extern_weak void @"_swift_FORCE_LOAD_$_swiftCompatibility56"()
+
+// BACKDEPLOY_CONCURRENCY: declare extern_weak swiftcc i8 @"$sScP8rawValues5UInt8Vvg"
 
 // OPTIMIZED: @swift_async_extendedFramePointerFlags = extern_weak global i8*
 // OPTIMIZED: @_swift_async_extendedFramePointerFlagsUser = linkonce_odr hidden global i8** @swift_async_extendedFramePointerFlags