Bootstrap failure on x86_64 possibly due to your change

[Richard Kenner]

When compiling par.adb, we get the assembler line:

        call    *$par__labl__find_enclosing_body.5842   # 181   *call_value_1_rex64     [length = 5]

which produces:

don% as -o par.o par.s
par.s: Assembler messages:
par.s:32076: Error: immediate operand illegal with absolute jump

I'm suspicious of the predicate changes in the x86 config directory as
the cause for this, though the one for the insn looks right to me at
first look.