[PPC] In PPCBoolRetToInt change the bool value to i64 if the target is ppc64

In PPCBoolRetToInt bool value is changed to i32 type. On ppc64 it may introduce an extra zero extension for the return value. This patch changes the integer type to i64 to avoid the zero extension on ppc64.

This patch fixed PR32442.

Differential Revision: https://reviews.llvm.org/D31407

llvm-svn: 298955