Fix unaligned memory read issue exposed by ubsan

Indexed profile data as designed today does not guarantee
counter data to be well aligned, so reading needs to use
the slower form (with memcpy). This is less than ideal and
should be improved in the future (i.e., with fixed length
function key instead of variable length name key).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@253309 91177308-0d34-0410-b5e6-96231b3b80d8