lang/scm: fix build on powerpc64*

(#<primitive-procedure call-with-current-continuation> #<CLOSURE <anon> "r4rstest.scm": (exit) (for-each (lambda (x) (if (negative? x) (exit x))) (quote (54 0 37 -3 245 19))) #t>) ==>
;ERROR: "r4rstest.scm": segment violation 11
; in expression: (#@apply #@fun #@args)
; in scope:
; (expect fun . args) procedure test
; defined by load: "r4rstest.scm"

;STACK TRACE
1; (#@let ((res (#@if (#@procedure? #@0+1) (#@apply #@0+1 #@0-2) ...
2; (#@test -3 #@call-with-current-continuation (#@lambda (exit) ( ...
3; (#@define ((filesuf #@file) (hss (#@has-suffix? #@file (#@sche ...
4; ((#@thunk) (#@set! #@complete #t))
5; ((#@do-thunk (#@lambda () (#@cond (#@*syntax-rules* (require ( ...
6; ((#@case #@option #(#<unspecified> #f #\? #\: #\n #\u #\m #\s ...
7; ((#@cond ((#@not #@*argv*) (#@set! #@*argv* (#@program-argumen ...

; program args: ("./scm" "-rmacro" "-fsyntest1.scm" "-fsyntest2.scm" "-fr4rstest.scm" "-e(test-sc4)(test-cont)(test-delay)" "-fsyntest1" "-e" "(or (null? errs) (quit 1))")

Builds fine with GCC.

While here, remove ia64 support.