Fix another infinite loop in InstCombine

Summary:
InstCombine infinite-loops for the testcase added
It is because InstCombine is generating instructions that can be
optimized by itself. Fix by not optimizing frem if the optimized
type is the same as original type.
rdar://problem/19150820

Reviewers: majnemer

Differential Revision: http://reviews.llvm.org/D6634