* grub-core/kern/x86_64/efi/startup.S (_start): Align the stack to a
    	16-byte boundary, as required by the x86-64 ABI, before calling
    	grub_main.  In some cases, GCC emits code that assumes this
    	alignment, which crashes if not aligned.  The EFI firmware is also
    	entitled to assume that stack alignment without checking.