[clang] [llvm] [DebugInfo] Emit DW_AT_const_value for constexpr array static members (PR #182442)

[Shivam Kunwar via cfe-commits]

phyBrackets wrote:

> > On an actual LLVM source file (CommandLine.cpp), the diff is literally zero, no constexpr array static members, no cost.
> 
> It would be more interesting to see how this change affects an existing, larger codebase. Could you compare the debug info size of the bin/clang binary built with vs without your change?

Alright so built clang with `RelWithDebInfo` and compared the full binary with and without the patch:

```
bloaty clang-after -- clang-before -d sections
    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0% +36.7Ki  [ = ]       0    .debug_info
  +0.0% +57.2Ki  +0.0% +2.14Ki    TOTAL
  ```
36.7KB of debug_info growth across the entire clang binary, rounding to +0.0%. The .text increase (~2KB) is from the new codegen in the two source files touched by the patch. Practically that seems like no measurable impact on debug info size.

https://github.com/llvm/llvm-project/pull/182442