[boot] Improve non-printing error handling

Add an implicit __LINE__ to the try_or_raise macro, which gets set in
r11 on cpu_assert. Also made status lines smarter about when to call
cpu_assert.

src/boot/main.cpp

@@ -163,7 +163,7 @@ uefi_preboot(uefi::handle image, uefi::system_table *st)
 memory::efi_mem_map
 uefi_exit(args::header *args, uefi::handle image, uefi::boot_services *bs)
 {
-	status_line status {L"Exiting UEFI"};
+	status_line status {L"Exiting UEFI", nullptr, false};
 
 	memory::efi_mem_map map =
 		memory::build_kernel_mem_map(args, bs);