1.0.41.24: ppc: Calling-convention fixes for entry-point handling during named-call.

1.0.41.24: ppc: Calling-convention fixes for entry-point handling during named-call.

  * For GC purposes, seven times never load reg_LIP before loading
whatever register points to the object it refers to.

  * During named-call, load the function from the fdefn before
loading the raw-addr (which ends up in reg_LIP).  For simple-fun
objects, this provides the reference base for reg_LIP.  For other
objects this doesn't matter because reg_LIP ends up pointing to
either undefined_tramp or closure_tramp.

  * This still leaves a race condition when updating fdefinitions,
but fixes the race condition surrounding function calling.

  * To fix the remaining race condition, we would need to alter
the undefined function trampoline to appear to be a simple-fun
object and adjust the fdefn-fun accessors to compensate, then
arrange for "named" calls to load reg_LEXENV and do closure-fun
access in the same manner as the closure_tramp and the "unnamed"
call VOPs.  This would add another instruction to the call path,
but not another memory access (as we would trade off loading the
fdefn-raw-addr for loading the closure-fun).