SwiftDriver: avoid using toSwiftString for target info

The C-String to Swift-String conversion would corrupt the path on
Windows, where the path separator would get dropped.  This would result
in the inability to use the driver due to the failure to load the
standard library as the SDK would not be consulted.

Directly convert the raw buffer to a `Data` for the foreign
representation.  Note that this also makes the code clearer as we
explicitly see the copying as opposed to the use of the deprecated
`String(bytesNoCopy:length:encoding:freeWhenDone:)` function.

Thanks to @artemcm for the help with this!

Author: compnerd

Sources/SwiftDriver/SwiftScan/SwiftScan.swift

@@ -339,14 +339,15 @@ internal extension swiftscan_diagnostic_severity_t {
                                              invocationStringArray)
     }
 
-    let targetInfoString: String = try compilerExecutablePath.description.withCString { cstring in
-      let targetInfoStringRef = api.swiftscan_compiler_target_info_query_v2(invocation, cstring)
-      defer { api.swiftscan_string_dispose(targetInfoStringRef) }
-      return try toSwiftString(targetInfoStringRef)
+    return try compilerExecutablePath.description.withCString {
+      let info = api.swiftscan_compiler_target_info_query_v2(invocation, $0)
+      defer { api.swiftscan_string_dispose(info) }
+      guard let data = info.data else {
+        throw DependencyScanningError.invalidStringPtr
+      }
+      return Data(buffer: UnsafeBufferPointer(start: data.bindMemory(to: CChar.self, capacity: info.length),
+                                              count: info.length))
     }
-
-    let targetInfoData = Data(targetInfoString.utf8)
-    return targetInfoData
   }
 }