ARM: whitespace

Remove some whitespace.  NFC.
Target: change member from reference to pointer

This is a preliminary step to help ease the construction of CallLoweringInfo.
Changing the construction to a chained function pattern requires that the
parameter be nullable.  However, rather than copying the vector, save a pointer
rather than the reference to permit a late binding of the arguments.
Target: add support to build CallLoweringInfo

Rather than introducing an auxiliary CallLoweringInfoBuilder, add the methods to
do chained function construction directly to CallLoweringInfo.  This reduces the
monstrous 15-parameter constructor into a series of simpler (for some definition
of simpler) functions that control particular aspects of the call.  The old
interfaces can be completely removed once callers are moved to the new chained
constructor pattern.
Target: remove old constructors for CallLoweringInfo

This is mostly a mechanical change changing all the call sites to the newer
chained-function construction pattern.  This removes the horrible 15-parameter
constructor for the CallLoweringInfo in favour of setting properties of the call
via chained functions.  No functional change beyond the removal of the old
constructors are intended.