[PGO] Don't set the function hotness attribute when populating counters

Don't set the function hotness attribute on the fly. This changes the CFG
branch probability of the caller function, which leads to inconsistent BB
ordering. This patch moves the attribute setting to a separated loop after
 the counts in all functions are populated.

Fixes PR27024 - PGO instrumentation profile data is not reflected in correct
basic blocks.

Differential Revision: http://reviews.llvm.org/D18491

llvm-svn: 264594