make SectionKindForGlobal target independent, and therefore non-virtual.

make SectionKindForGlobal target independent, and therefore non-virtual.
It's classifications now include elf-specific discriminators.  Targets
that don't have these features (like darwin and pecoff) simply treat
data.rel like data, etc.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@76993 91177308-0d34-0410-b5e6-96231b3b80d8