Have the ELF symbol predicates match more directly the spec.

The underlaying issues is that this code can't really know if an OS specific or
processor specific section number should return true or false.

One option would be to assert or return an error, but that looks like over
engineering since extensions are not that common.

It seems better to have these be direct implementation of the ELF spec so that
they are natural for someone familiar with ELF reading the code.

Code that does have to handle OS/Architecture specific values can do it at
a higher level.

llvm-svn: 239618