[ProfileSummary] Count callsite samples when computing total samples.

Summary: Currently ProfileSummaryBuilder doesn't count into callsite samples when computing total samples. Considering that ProfileSummaryInfo is used to checked the hotness of not only body samples but also callsite samples (from SampleProfileLoader), I think the callsite sample counts should be considered when computing total samples.

Reviewers: eraman, danielcdh, wmi

Subscribers: hiraditya, jdoerfert, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59835

llvm-svn: 357627