Treat lines in projectMap.csv that start with '#' as comments. This enables a
workflow where projects can be temporarily disabled with a comment describing
when they should be turned back on.

Differential Revision: https://reviews.llvm.org/D24709

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@281880 91177308-0d34-0410-b5e6-96231b3b80d8