LLVM/Clang Warnings - Fixed Warnings

Fixed Warnings

FileLinePriorityTypeCategory
SampleProfReader.h659NormalClang (LLVM based)-Winconsistent-missing-override
SampleProfReader.h698NormalClang (LLVM based)-Winconsistent-missing-override
AVRFrameLowering.cpp55NormalClang (LLVM based)-Wunused-variable