MFC r357232:

Merge r357231 from the clang1000-import branch:

Work around assembler error from clang 10.0.0 in gptboot:

stand/i386/gptboot/gptldr.S:141:3: error: value of 36878 is too large for field of 2 bytes.

jmp MEM_JMP # Start BTX
^

Use the same construct as in stand/i386/boot2/boot1.S, which ensures the
jump distance does not become too large.