SampleProfile.cpp: Quick fix to r203976 about abuse of Twine. The life of Twine was too short.

FIXME: DiagnosticInfoSampleProfile should not hold Twine&.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203990 91177308-0d34-0410-b5e6-96231b3b80d8