[llvm] Add DISubrangeType (PR #126772)

[Tom Tromey via llvm-commits]

tromey wrote:

Maybe worth pointing out that the bias extension is being standardized: https://dwarfstd.org/issues/190809.1.html

When DWARF 6 is released this will be an easy fix.

Pierre-Marie documented the extension when it was added to GCC: https://gcc.gnu.org/wiki/DW_AT_GNU_bias

https://github.com/llvm/llvm-project/pull/126772