libdiscid: update to 0.6.4.

libdiscid-0.6.4:

- LIB-69: Revert "Use discid_feature enum in discid_read_sparse". Fixes
  compiler errors with C++.

libdiscid-0.6.3:

- LIB-66: fix for Debian kFreeBSD
- Haiku platform support (TOC only)
- Use discid_feature enum in discid_read_sparse
- Fixed building with CMake on macOS
- LIB-68: provide macOS universal2 binaries with support for both
          x86_64 and arm64
- LIB-67: Source tarball with updated autotools configuration
- CMake: Use GNUInstallDirs to determine install location
- CMake 2.8.12 is now the minimum required version

(wiz)