Make JIT inline cast_for_multi_block_arg correctly
Make JIT inline cast_for_multi_block_arg correctly

(Bug originally found in rbx-1.3.3)

JIT was not inlining arguments correctly when given more than one
argument, and would end up yielding cUndef (Object:0x22) instead.

See https://gist.github.com/sshao/7eecc87458d3e55d7f5d
(run on rbx-1.3.3) for examples.

ruipserra/rubinius,heftig/rubinius,digitalextremist/rubinius,mlarraz/rubinius,heftig/rubinius,ruipserra/rubinius,jsyeo/rubinius,Azizou/rubinius,ruipserra/rubinius,dblock/rubinius,jemc/rubinius,benlovell/rubinius,mlarraz/rubinius,jsyeo/rubinius,sferik/rubinius,dblock/rubinius,benlovell/rubinius,mlarraz/rubinius,heftig/rubinius,heftig/rubinius,benlovell/rubinius,jsyeo/rubinius,jemc/rubinius,kachick/rubinius,Wirachmat/rubinius,ruipserra/rubinius,mlarraz/rubinius,digitalextremist/rubinius,digitalextremist/rubinius,ruipserra/rubinius,jemc/rubinius,benlovell/rubinius,jemc/rubinius,heftig/rubinius,Wirachmat/rubinius,sferik/rubinius,jsyeo/rubinius,benlovell/rubinius,Azizou/rubinius,digitalextremist/rubinius,jemc/rubinius,dblock/rubinius,Azizou/rubinius,kachick/rubinius,kachick/rubinius,kachick/rubinius,dblock/rubinius,digitalextremist/rubinius,jemc/rubinius,Azizou/rubinius,Wirachmat/rubinius,Wirachmat/rubinius,ngpestelos/rubinius,Azizou/rubinius,sferik/rubinius,digitalextremist/rubinius,jsyeo/rubinius,sferik/rubinius,kachick/rubinius,mlarraz/rubinius,dblock/rubinius,kachick/rubinius,jsyeo/rubinius,heftig/rubinius,ngpestelos/rubinius,jsyeo/rubinius,benlovell/rubinius,ruipserra/rubinius,sferik/rubinius,ngpestelos/rubinius,ngpestelos/rubinius,Azizou/rubinius,sferik/rubinius,Wirachmat/rubinius,Wirachmat/rubinius,sferik/rubinius,dblock/rubinius,mlarraz/rubinius,benlovell/rubinius,ngpestelos/rubinius,ngpestelos/rubinius,kachick/rubinius,mlarraz/rubinius,dblock/rubinius,ngpestelos/rubinius,Wirachmat/rubinius,ruipserra/rubinius,Azizou/rubinius,digitalextremist/rubinius,jemc/rubinius,heftig/rubinius,kachick/rubinius