[ELF] - Never create .gnu_hash with NBuckets == 0.

Currently, we can end up with NBuckets==0 and android loader
does not like it (PR36537).

Seems we can go with a minimal amount of changes here for simplicity
and be consistent with gold and so just always use >= 1 value for NBuckets.

Differential revision: https://reviews.llvm.org/D44422

llvm-svn: 327481