Fix autosplat conditions to handle ruby2_keywords case

	Autosplat should not occur if there are two arguments but second
	argument is an array containing a ruby2_keywords splat. Only
	autosplat if a single argument to be yielded to the block, and there
	is no splatted flagged keyword hash passed.

	Fixes [Bug #19759]
	---
	 test/ruby/test_proc.rb | 26 ++++++++++++++++++++++++++
	 vm_args.c              |  3 ++-
	 2 files changed, 28 insertions(+), 1 deletion(-)

rb_ary_tmp_new suggests that the array is temporary in some way, but
that's not true, it just creates an array that's hidden and not on the
transient heap. This commit renames it to rb_ary_hidden_new.

[Misc #18891]

For a method such as:

  def foo(*callee_args) end

If this method is called with a flagged hash (created by a method
flagged with ruby2_keywords), this previously passed the hash
through without modification.  With this change, it acts as if the
last hash was passed as keywords, so a call to:

  foo(*caller_args)

where the last element of caller_args is a flagged hash, will be
treated as:

  foo(*caller_args[0...-1], **caller_args[-1])

As a result, inside foo, callee_args[-1] is an unflagged duplicate
of caller_args[-1] (all other elements of callee_args match
caller_args).

Fixes [Bug #18625]

If the block only accepts a single positional argument plus keywords,
then do not autosplat.  Still autosplat if the block accepts more
than one positional argument in addition to keywords.

Autosplatting a single positional argument plus keywords made sense
in Ruby 2, since a final positional hash could be used as keywords,
but it does not make sense in Ruby 3.

Fixes [Bug #18633]

Use ISEQ_BODY macro to get the rb_iseq_constant_body of the ISeq. Using
this macro will make it easier for us to change the allocation strategy
of rb_iseq_constant_body when using Variable Width Allocation.

Linking printf family functions makes mjit objects to link
unnecessary code.