[fusl] Remove code for unsupported architectures

fusl/src/thread/powerpc/clone.s

-.text
-.global __clone
-.type __clone, %function
-__clone:
-# int clone(fn, stack, flags, arg, ptid, tls, ctid)
-#            a  b       c     d     e    f    g
-#            3  4       5     6     7    8    9
-# pseudo C code:
-# tid = syscall(SYS_clone,c,b,e,f,g);
-# if (!tid) syscall(SYS_exit, a(d));
-# return tid;
-
-# SYS_clone = 120
-# SYS_exit = 1
-
-# store non-volatile regs r30, r31 on stack in order to put our
-# start func and its arg there
-stwu 30, -16(1)
-stw 31, 4(1)
-
-# save r3 (func) into r30, and r6(arg) into r31
-mr 30, 3
-mr 31, 6
-
-#move c into first arg
-mr 3, 5
-#mr 4, 4
-mr 5, 7
-mr 6, 8
-mr 7, 9
-
-# move syscall number into r0    
-li 0, 120
-
-sc
-
-# check for syscall error
-bns+ 1f # jump to label 1 if no summary overflow.
-#else
-neg 3, 3 #negate the result (errno)
-1:
-# compare sc result with 0
-cmpwi cr7, 3, 0
-
-# if not 0, jump to end
-bne cr7, 2f
-
-#else: we're the child
-#call funcptr: move arg (d) into r3
-mr 3, 31
-#move r30 (funcptr) into CTR reg
-mtctr 30
-# call CTR reg
-bctrl
-# mov SYS_exit into r0 (the exit param is already in r3)
-li 0, 1
-sc
-
-2:
-
-# restore stack
-lwz 30, 0(1)
-lwz 31, 4(1)
-addi 1, 1, 16
-
-blr
-