Workspace,Build: reduce mtime updates

When building a project inside of VSCode with the LSP enabled,
rebuilding the project would trigger a change to the mtimes of the
auxiliary files resulting in an unnecessary rebuilding of targets.  In
conjunction with the changes to tools-support-core
(swiftlang/swift-tools-support-core#422), incremental builds do not trigger
a cascade of rebuilds that are unnecessary.

Extracted from a patch by Ami Fischman!

Sources/Build/BuildOperationBuildSystemDelegateHandler.swift

@@ -517,7 +517,7 @@ final class WriteAuxiliaryFileCommand: CustomLLBuildCommand {
         }
 
         do {
-            try self.context.fileSystem.writeFileContents(outputFilePath, string: getFileContents(tool: tool))
+            try self.context.fileSystem.writeIfChanged(path: outputFilePath, string: getFileContents(tool: tool))
             return true
         } catch {
             self.context.observabilityScope.emit(error: "failed to write auxiliary file '\(outputFilePath.pathString)': \(error.interpolationDescription)")

Sources/Workspace/Workspace+State.swift

@@ -135,7 +135,7 @@ fileprivate struct WorkspaceStateStorage {
             let storage = V6(dependencies: dependencies, artifacts: artifacts)
 
             let data = try self.encoder.encode(storage)
-            try self.fileSystem.writeFileContents(self.path, data: data)
+            try self.fileSystem.writeIfChanged(path: self.path, bytes: .init(data))
         }
     }