[PGO][PGSO] Fix -DBUILD_SHARED_LIBS=on builds after D69580/llvmorg-10-init-8797-g0d987e411ac

Move TargetLoweringBase::isSuitableForJumpTable from
llvm/CodeGen/TargetLowering.h to .cpp, to avoid the undefined reference
from all LLVM${Target}ISelLowering.cpp.

Another fix is to add a dependency on TransformUtils to all
lib/Target/$Target/LLVMBuild.txt, but that is too disruptive.