Build: migrate to file lists for driver invocations

When invoking the driver use file lists rather than passing all the
sources on the command line.  This is particularly import for Windows
where the command line limit is 32k.  With deep dependency sets and
large projects, it is possible to overrun this limit and fail to invoke
the command.  The driver itself will invoke the frontend using response
files if the invocation will overflow the command line limit.

Author: compnerd

Sources/Build/BuildDescription/SwiftTargetBuildDescription.swift

@@ -546,7 +546,8 @@ public final class SwiftTargetBuildDescription {
         }
 
         result.append("-c")
-        result.append(contentsOf: self.sources.map(\.pathString))
+        // FIXME: Eliminate side effect.
+        try result.append("@\(self.writeFileList().pathString)")
 
         result.append("-I")
         result.append(self.buildParameters.buildPath.pathString)
@@ -578,9 +579,8 @@ public final class SwiftTargetBuildDescription {
 
         // FIXME: Handle WMO
 
-        for source in self.target.sources.paths {
-            result.append(source.pathString)
-        }
+        // FIXME: Eliminate side effect.
+        try result.append("@\(self.writeFileList(for: self.target).pathString)")
 
         result.append("-I")
         result.append(self.buildParameters.buildPath.pathString)
@@ -631,9 +631,8 @@ public final class SwiftTargetBuildDescription {
         // FIXME: Handle WMO
 
         result.append("-c")
-        for source in self.target.sources.paths {
-            result.append(source.pathString)
-        }
+        // FIXME: Eliminate side effect.
+        try result.append("@\(self.writeFileList(for: self.target).pathString)")
 
         result.append("-I")
         result.append(self.buildParameters.buildPath.pathString)
@@ -761,6 +760,20 @@ public final class SwiftTargetBuildDescription {
         return path
     }
 
+    private func writeFileList() throws -> AbsolutePath {
+        let path = self.tempsPath.appending(component: "sources.filelist")
+        let contents = self.sources.map { $0.pathString.spm_shellEscaped() }.joined(separator: "\n")
+        try self.fileSystem.writeFileContents(path, string: contents)
+        return path
+    }
+
+    private func writeFileList(for target: Target) throws -> AbsolutePath {
+        let path = self.tempsPath.appending(component: "\(target.name)-sources.filelist")
+        let contents = target.sources.paths.map { $0.pathString.spm_shellEscaped() }.joined(separator: "\n")
+        try self.fileSystem.writeFileContents(path, string: contents)
+        return path
+    }
+
     /// Generates the module map for the Swift target and returns its path.
     private func generateModuleMap() throws -> AbsolutePath {
         let path = self.tempsPath.appending(component: moduleMapFilename)