In similar vein to b6ef167564, add pg_lfind8() and pg_lfind8_le() to search for bytes equal or less-than-or-equal to a given byte, respectively. To abstract away platform details, add helper functions and typedefs to simd.h. John Naylor and Nathan Bossart, per suggestion from Andres Freund Discussion: https://www.postgresql.org/message-id/CAFBsxsGzaaGLF%3DNuq61iRXTyspbO9rOjhSqFN%3DV6ozzmta5mXg%40mail.gmail.com
b6ef167564