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

[Shivam Kunwar via llvm-commits]

phyBrackets wrote:

> I'd be curious of the use-case. LLDB seems to be able to read the contents of the static just fine (even at `-O3`):
> 
> ```
> struct Test {
> static inline constexpr char TEST[] = "Test String";
> };
> 
> int main() {
>     __builtin_printf("%s", Test::TEST);
>     __builtin_debugtrap();
> }
> ```
> 
> ```
> warning: a.out was compiled with optimization - stepping may behave oddly; variables may not be available.
> (lldb) v Test::TEST
> (const char[12]) Test::TEST = "Test String"
> ```

@Michael137 Thanks for taking a look! lldb can read the value when the variable still exists in memory, but I think `DW_AT_const_value`  helps in cases where it doesn't for eg if the variable is never odr used, the linker can discard it entirely, and there would be no memory location to read, and remote debugging where reading target memory is expensive or unavailable. 

And GCC already emits this, so there's a compatibility argument, but if others think the dwarf size cost isn't worth it for this cases, then i am happy to discus this further

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