llvm: always include debug information for global variables

[pkova]

Fixes #15095

Somebody who knows these compiler internals should verify my logic here, but the conditional here does not make sense to me. Consider the following piece of code example.zig:

var globl: i32 = 0;

pub fn main() void {
    var hello: i32 = 1;
    hello += 1;
    globl += 124;
}

globl is the variable that debuggers cannot find. On master this is the relevant LLVM IR:

@example.globl = internal unnamed_addr global i32 0, align 4

With my fix this becomes:

@example.globl = internal unnamed_addr global i32 0, align 4, !dbg !13

Note the !dbg that was speculated to be the cause in the issue as well. I've verified that this fix allows debuggers to see non-exported global variables, but I'm still confused as to why this check ever existed.