Add _cdio_strdup_fixpath for absolute paths handling in MinGW

* MinGW may provide absolute paths in the form /c/directory/...
  to native calls that require instead c:/directory

include/cdio/util.h

@@ -99,6 +99,12 @@ _cdio_memdup (const void *mem, size_t count);
 char *
 _cdio_strdup_upper (const char str[]);
 
+/* Duplicate path and make it platform compliant. Typically needed for
+   MinGW/MSYS where a "/c/..." path must be translated to "c:/..." for
+   use with fopen(), etc. Returned string must be freed by the caller. */
+char * 
+_cdio_strdup_fixpath (const char path[]);
+
 void
 _cdio_strfreev(char **strv);