Require a base pointer for stack realignment when SP may vary dynamically.

ARMBaseRegisterInfo::canRealignStack was checking for variable-sized objects
but not for stack adjustments around calls.  Use hasReservedCallFrame() to
check for both.  The hasBasePointer function was already correctly checking
both conditions, so the effect of this was that a base pointer would be used
without checking whether the base pointer register could be reserved. I don't
have a small testcase for this.

<rdar://problem/11075906>

llvm-svn: 153110