[libcalamares] Special-case for not-for-dash-o options

- The unpackfs module uses this to --bind-mount things
   without options.

src/libcalamares/partition/Mount.cpp

@@ -58,7 +58,7 @@ mount( const QString& devicePath, const QString& mountPoint, const QString& file
         }
     }
 
-    QStringList args = { "mount", devicePath, mountPoint };
+    QStringList args = { "mount" };
 
     if ( !filesystemName.isEmpty() )
     {
@@ -66,8 +66,16 @@ mount( const QString& devicePath, const QString& mountPoint, const QString& file
     }
     if ( !options.isEmpty() )
     {
-        args << "-o" << options;
+        if ( options.startsWith( '-' ) )
+        {
+            args << options;
+        }
+        else
+        {
+            args << "-o" << options;
+        }
     }
+    args << devicePath << mountPoint;
 
     auto r = CalamaresUtils::System::runCommand( args, 10 );
     sync();

src/libcalamares/partition/Mount.h

@@ -36,6 +36,8 @@ namespace Partition
  * @param mountPoint the full path of the target mount point.
  * @param filesystemName the name of the filesystem (optional).
  * @param options any additional options as passed to mount -o (optional).
+ *          If @p options starts with a dash (-) then it is passed unchanged
+ *          and no -o option is added; this is used in handling --bind mounts.
  * @returns the program's exit code, or:
  *             Crashed = QProcess crash
  *             FailedToStart = QProcess cannot start