Make PackageModel resources optional (#7348)

#7337 is breaking
toolchain builds, so we should pass `SKIP_RESOURCE_SUPPORT` by default
to avoid that.

Author: MaxDesiatov

Package.swift

@@ -73,6 +73,19 @@ automatic linking type with `-auto` suffix appended to product's name.
 */
 let autoProducts = [swiftPMProduct, swiftPMDataModelProduct]
 
+
+let packageModelResourcesSettings: [SwiftSetting]
+let packageModelResources: [Resource]
+if ProcessInfo.processInfo.environment["SWIFTPM_USE_LIBRARIES_METADATA"] == nil {
+    packageModelResources = []
+    packageModelResourcesSettings = [.define("SKIP_RESOURCE_SUPPORT")]
+} else {
+    packageModelResources = [
+        .copy("InstalledLibrariesSupport/provided-libraries.json"),
+    ]
+    packageModelResourcesSettings = []
+}
+
 let package = Package(
     name: "SwiftPM",
     platforms: [
@@ -218,9 +231,8 @@ let package = Package(
             name: "PackageModel",
             dependencies: ["Basics"],
             exclude: ["CMakeLists.txt", "README.md"],
-            resources: [
-                .copy("InstalledLibrariesSupport/provided-libraries.json"),
-            ]
+            resources: packageModelResources,
+            swiftSettings: packageModelResourcesSettings
         ),
 
         .target(

Sources/PackageModel/UserToolchain.swift

@@ -545,7 +545,7 @@ public final class UserToolchain: Toolchain {
         if let customProvidedLibraries {
             self.providedLibraries = customProvidedLibraries
         } else {
-            // When building with CMake, we need to skip resource support.
+            // When building with CMake or `swift build --build-system xcode`, we need to skip resource support.
             #if SKIP_RESOURCE_SUPPORT
             let path = self.swiftCompilerPath.parentDirectory.parentDirectory.appending(components: ["share", "pm", "provided-libraries.json"])
             #else