Code to replace path separators on DOS-based filesystems is invalid

[CohenArthur]

  // On windows, the path might mix '/' and '\' separators. Replace the
  // UNIX-like separators by MSDOS separators to make sure the path will resolve
  // properly.
  //
  // Source: rustc compiler
  // (https://github.com/rust-lang/rust/blob/9863bf51a52b8e61bcad312f81b5193d53099f9f/compiler/rustc_expand/src/module.rs#L174)
#if defined(HAVE_DOS_BASED_FILE_SYSTEM)
  path.replace ('/', '\\');
#endif /* HAVE_DOS_BASED_FILE_SYSTEM */

this code is invalid, and throws an error about a lack of matching function. https://en.cppreference.com/w/cpp/string/basic_string/replace shows that indeed this is not a correct usage of the function, and that we should change it.

[CohenArthur]

This is also mentioned in #2843 and can be replaced with a call to std::replace

[CohenArthur]

Assigning this to myself because this has been fixed by a patch from a GCC contributor, which I need to tweak and push here as a PR