[SampleFDO] Extend profile-sample-accurate option to cover isFunctionColdInCallGraph

For SampleFDO, when a callsite doesn't appear in the profile, it will not be marked as cold callsite unless the option -profile-sample-accurate is specified.

But profile-sample-accurate doesn't cover function isFunctionColdInCallGraph which is used to decide whether a function should be put into text.unlikely section, so even if the user knows the profile is accurate and specifies profile-sample-accurate, those functions not appearing in the sample profile are still not be put into text.unlikely section right now.

The patch fixes that.

Differential Revision: https://reviews.llvm.org/D55567

llvm-svn: 348940