[llvm-lipo] Relax the check of the specified input file architecture

cctools lipo only compares the cputypes when it verifies that
the specified (via -arch) input file and the architecture match.
This diff adjusts the behavior of llvm-lipo accordingly. 

Differential revision: https://reviews.llvm.org/D68319

Test plan: make check-all

llvm-svn: 373966