tests: avoid loading 16 MiB onto the stack

Currently, Zig semantically loads an array as a temporary when indexing
it. This means it cannot be guaranteed that only the requested element
is loaded; in particular, our self-hosted backends do not elide the load
of the full array, so this test case was crashing on self-hosted.

test/link/bss/main.zig

@@ -6,8 +6,9 @@ var buffer: [0x1000000]u64 = [1]u64{0} ** 0x1000000;
 pub fn main() anyerror!void {
     buffer[0x10] = 1;
     try std.io.getStdOut().writer().print("{d}, {d}, {d}\n", .{
-        buffer[0],
-        buffer[0x10],
-        buffer[0x1000000 - 1],
+        // workaround the dreaded decl_val
+        (&buffer)[0],
+        (&buffer)[0x10],
+        (&buffer)[0x1000000 - 1],
     });
 }