Fix Generic_GCC::GCCVersion::operator<

Without this patch comparing two equal versions without patch numbers (4.7 for
example) will result in A < B and B < A.

Patch by Simon Atanasyan.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@170705 91177308-0d34-0410-b5e6-96231b3b80d8