[InstCombine] Move class into anonymous namespace. NFC.

This is necessary to avoid warnings from GCC.
InstCombineLoadStoreAlloca.cpp:238:7: error: 'PointerReplacer' declared
with greater visibility than the type of its field 'PointerReplacer::IC'

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@294794 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed