If enabled, this will attempt to use the CC_LOG_DIAGNOSTICS feature I dropped
into Clang to print a log of all the diagnostics generated during an individual
build (from the top-level). Not sure if this will actually be useful, but for
now it is handy for testing the option.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129312 91177308-0d34-0410-b5e6-96231b3b80d8
