spirv: enable simplified default panic handler

SPIR-V cannot print, so we cannot yet use the fancy default
panic handler. Instead we will just use the infinite loop
one for now.

lib/std/builtin.zig

@@ -741,7 +741,8 @@ pub fn default_panic(msg: []const u8, error_return_trace: ?*StackTrace, ret_addr
         builtin.zig_backend == .stage2_x86_64 or
         builtin.zig_backend == .stage2_x86 or
         builtin.zig_backend == .stage2_riscv64 or
-        builtin.zig_backend == .stage2_sparc64)
+        builtin.zig_backend == .stage2_sparc64 or
+        builtin.zig_backend == .stage2_spirv64)
     {
         while (true) {
             @breakpoint();