Second patch of patch series that improves MergeFunctions performance time from O(N*N) to

O(N*log(N)). The idea is to introduce total ordering among functions set.
It allows to build binary tree and perform function look-up procedure in O(log(N)) time. 

This patch description:
Introduced total ordering among constants implemented in cmpConstants method.
Method performs lexicographical comparison between constants represented as
hypothetical numbers of next format:
<bitcastability-trait><raw-bit-contents>

Please, read cmpConstants declaration comments for more details.

llvm-svn: 208173