[CodeGen][ARM] Make sure the value and type used to create a bitcast

have the same size.

This fixes an asset that is triggered when an address of a boolean
variable is passed to __builtin_arm_ldrex or __builtin_arm_strex.

rdar://problem/29269006


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@288404 91177308-0d34-0410-b5e6-96231b3b80d8