Unblock SwiftPM's build

This fixes two issues:
- First one is the same as #2875
- Second one is a crash related to build conditionals which looks like a
longer standing bug that was triggered by swiftlang/swift-llbuild#681
Unforunately, llbuild CI doesn't test the package, so it slipped through
and now causes SwiftPM to crash when building itself

Author: neonichu

Sources/PackageLoading/PackageBuilder.swift

@@ -840,12 +840,12 @@ public final class PackageBuilder {
     func buildConditions(from condition: PackageConditionDescription?) -> [PackageConditionProtocol] {
         var conditions: [PackageConditionProtocol] = []
 
-        if let config = condition?.config.map({ BuildConfiguration(rawValue: $0)! }) {
+        if let config = condition?.config.flatMap({ BuildConfiguration(rawValue: $0) }) {
             let condition = ConfigurationCondition(configuration: config)
             conditions.append(condition)
         }
 
-        if let platforms = condition?.platformNames.map({ platformRegistry.platformByName[$0]! }), !platforms.isEmpty {
+        if let platforms = condition?.platformNames.flatMap({ platformRegistry.platformByName[$0] }), !platforms.isEmpty {
             let condition = PlatformsCondition(platforms: platforms)
             conditions.append(condition)
         }

Sources/SPMTestSupport/MockDownloader.swift

@@ -49,6 +49,7 @@ public class MockDownloader: Downloader {
     public func downloadFile(
         at url: Foundation.URL,
         to destinationPath: AbsolutePath,
+        withAuthorizationProvider: AuthorizationProviding? = nil,
         progress: @escaping Downloader.Progress,
         completion: @escaping Downloader.Completion
     ) {

Sources/Workspace/Workspace.swift

@@ -1421,6 +1421,7 @@ extension Workspace {
             downloader.downloadFile(
                 at: parsedURL,
                 to: archivePath,
+                withAuthorizationProvider: nil,
                 progress: { bytesDownloaded, totalBytesToDownload in
                     self.delegate?.downloadingBinaryArtifact(
                         from: url,