Fix a bug that made the nightly tester *really* slow. During changes for

Fix a bug that made the nightly tester *really* slow. During changes for
portability, the --track-space option was inadvertently ignored. This patch
fixes that so that sys::Process::GetMallocUsage() is only invoked if the
--track-spaces option is given. Apparently the mallinfo() call that
GetMallocUsage() uses is *very* slow, especially when processing very large
modules like projects/llvm-test/MultiSource/Applications/kimwitu++.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@19163 91177308-0d34-0410-b5e6-96231b3b80d8