Fix the following warning when compiling with clang (caused by commit
rL343951):
GlobalsStream.cpp:61:33: warning: comparison of integers of different
signs: 'int' and 'uint32_t'
This also avoids double evaluation of `GlobalsTable.HashBuckets.size()`.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@343957 91177308-0d34-0410-b5e6-96231b3b80d8