Use options debug format if it is provided

[bentheklutz]

Closes #19478

As in the linked issue:

hello.zig

const std = @import("std");
pub fn main() void {
     std.debug.print("Hello, ziguana\n", .{});
}

Compilation and debug info

/home/bhetz -> zig build-obj -gdwarf64 -ODebug -target x86_64-linux hello.zig 
/home/bhetz -> objdump --dwarf=info hello.o | head -n 10

hello.o:     file format elf64-x86-64

Contents of the .debug_info section:

  Compilation Unit @ offset 0:
   Length:        0x3c779 (64-bit)
   Version:       4
   Abbrev Offset: 0
   Pointer Size:  8
/home/bhetz -> zig build-obj -gdwarf32 -ODebug -target x86-linux hello.zig 
/home/bhetz -> objdump --dwarf=info hello.o | head -n 10

hello.o:     file format elf32-i386

Contents of the .debug_info section:

  Compilation Unit @ offset 0:
   Length:        0x2c404 (32-bit)
   Version:       4
   Abbrev Offset: 0
   Pointer Size:  4

[bentheklutz]

Just to confirm the existing default behavior of 32bit dwarf for linux x64 remains.

/home/bhetz -> zig build-obj -ODebug -target x86_64-linux hello.zig 
/home/bhetz -> objdump --dwarf=info hello.o | head -n 10

hello.o:     file format elf64-x86-64

Contents of the .debug_info section:

  Compilation Unit @ offset 0:
   Length:        0x2e571 (32-bit)
   Version:       4
   Abbrev Offset: 0
   Pointer Size:  8

[alexrp]

It would be nice to return an error if the target object format doesn't support the specified debug format. But that would probably require some refactoring (e.g. moving DebugFormat to std.Target alongside ObjectFormat), so that's a problem for another day.

[bentheklutz]

Thanks for the feedback. I had the same concern about mismatching object and debug formats. I'd be happy to take a crack at that refactor here soon, but I should probably get through a few more contributor friendly issues first I think.