[ThinLTO] Save 8B per summary entry by rearranging the fields (NFC)

Size goes from 72B to 64B per entry.

Differential Revision: https://reviews.llvm.org/D27970

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@290314 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed