Upgrade LDC to 1.40.0
This merge request upgrades LDC to 1.40.0 with some other changes:
- Also builds on loong64 and mips64el
- Allow bootstrapping LDC using a previous version of LDC
- Run very basic unit tests after the build
- Explicitly set DWARF v4 to make DWZ happy (also fixes the Lintian warning)
- Add lld-19 and llvm-19-linker-tools as recommended packages for ldc (may fix some issues related to linkers on BTS)
- Update Debian standard version to v4.7.0
- Build and install both static and shared libraries in one step
Edited by Zixing Liu