[CMake] using ctest launchers leads to empty warning/error messages on the dashboard

[Matthias Kretz]

Hi,

using

  set(ENV{CTEST_USE_LAUNCHERS_DEFAULT} "ON")

I don't get any output on the CDash dashboard anymore. AFAICT the Build 
directory in Testing/tag/ is removed but never recreated. I.e. if I call

  CTEST_LAUNCH_LOGS=./not-existing-directory make

the launcher output is not stored to disk. With

  CTEST_LAUNCH_LOGS=./ make

I get launch-* and warning-* files in the cwd.

Is this a bug in ctest or am I doing something wrong? I was testing with cmake 
version 3.3.0-rc3.

Cheers,
	Matthias

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  Matthias Kretz
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