common, compiler: Upgrade to SystemPackage

For cross-platform support.

Signed-off-by: Will Hawkins <hawkinsw@obs.cr>

Sources/Common/SourceCode.swift

@@ -16,7 +16,7 @@
 // along with this program. If not, see <https://www.gnu.org/licenses/>.
 
 import Foundation
-import System
+import SystemPackage
 
 /// Represent a location in a post-preprocessed piece of P4 source code.
 public struct SourceLocation: Equatable, CustomStringConvertible {
@@ -145,9 +145,7 @@ func do_preprocess(
         }
 
         // Try to make a url from the configured file.
-        guard let included_url = URL.init(filePath: included_path) else {
-          return .Error(Error(withMessage: "Could not convert \(included_path) into a URL"))
-        }
+        let included_url = URL.init(filePath: included_path.string)
 
         // By calling ourselves recursively, the include being processed will
         // be _completely_ expanded (including any nested includes).
@@ -203,9 +201,7 @@ public struct SourceCodePreprocessor {
       return .Error(Error(withMessage: "Could not open \(file) for preprocessing"))
     }
 
-    guard let url = URL.init(filePath: file_to_open) else {
-      return .Error(Error(withMessage: "Could not convert \(file_to_open) into a URL"))
-    }
+    let url = URL.init(filePath: file_to_open.string)
 
     switch do_preprocess(url, self.manager) {
     case .Ok((let location, let contents)):