Make the API for adding targets string based so that it can easily
use cmGeneratorTarget.
Teach the cmIncludeCommand to generate the exported file at
configure-time instead if it is to be include()d.
The RunCMake.ExportWithoutLanguage test now needs a dummy header.h
file as expected error from export() is now reported after the
missing file error.
Set the minimum required version of CMake high enough to avoid the
warning for CMAKE_LEGACY_CYGWIN_WIN32. The warning appears on stderr
and breaks the expected output matching.
First, it prevents a NULL dereference and second it reiterates that
targets without languages are not supported by CMake.
Add a RunCMake.ExportWithoutLanguage test exporting a library without a
languages.