cmCTestLaunch first used an empty initializer list to zero-initialize a
buffer, but this is not supported on older compilers. Instead we avoid
the need for initialization altogether.
This creates an undocumented 'ctest --launch' mode. It launches a
specified command and optionally records a failure in an xml fragment.
We will optionally use this in CTest's Build stage to record per-rule
build failure information when using Makefile generators.
Brad King