$ ls /tmp/src/
CMakeLists.txt
$ cat /tmp/src/CMakeLists.txt
cmake_minimum_required(VERSION 3.3)
add_custom_command(OUTPUT empty.txt COMMAND touch empty.txt)
add_custom_target(mytarget DEPENDS empty.txt)
export(TARGETS mytarget FILE export.cmake)
$ mkdir /tmp/build
$ cd /tmp/build
$ ~/tmp/cmake-3.3.0-rc4-Linux-x86_64/bin/cmake /tmp/src
-- The C compiler identification is GNU 4.9.2
-- The CXX compiler identification is GNU 4.9.2
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
CMake Error in CMakeLists.txt:
  Exporting the target "mytarget" is not allowed since its linker language
  cannot be determined


CMake Internal Error (please report a bug) in CMakeLists.txt:
  cmTarget::GetOutputInfo called for mytarget which has type UTILITY

Note: The stack trace will not use advanced capabilities because this is a release build.
0x80ac96 : cmsys::SystemInformationImplementation::GetProgramStack(int, int) [(cmake) ???:-1]
0x80bc79 : cmsys::SystemInformation::GetProgramStack(int, int) [(cmake) ???:-1]
0x601d83 : displayMessage(cmake::MessageType, std::basic_ostringstream<char, std::char_traits<char>, std::allocator<char> >&) [(cmake) ???:-1]
0x609f9b : cmake::IssueMessage(cmake::MessageType, std::string const&, cmListFileContext const&) [(cmake) ???:-1]
0x575844 : cmMakefile::IssueMessage(cmake::MessageType, std::string const&) const [(cmake) ???:-1]
0x5de8f4 : cmTarget::GetOutputInfo(std::string const&) const [(cmake) ???:-1]
0x5e15b8 : cmTarget::GetDirectory(std::string const&, bool) const [(cmake) ???:-1]
0x5da483 : cmTarget::NormalGetFullPath(std::string const&, bool, bool) const [(cmake) ???:-1]
0x5e1549 : cmTarget::GetFullPath(std::string const&, bool, bool) const [(cmake) ???:-1]
0x70491b : cmExportBuildFileGenerator::SetImportLocationProperty(std::string const&, std::string const&, cmTarget*, std::map<std::string, std::string, std::less<std::string>, std::allocator<std::pair<std::string const, std::string> > >&) [(cmake) ???:-1]
0x704ea5 : cmExportBuildFileGenerator::GenerateImportTargetsConfig(std::ostream&, std::string const&, std::string const&, std::vector<std::string, std::allocator<std::string> >&) [(cmake) ???:-1]
0x705f4a : cmExportFileGenerator::GenerateImportConfig(std::ostream&, std::string const&, std::vector<std::string, std::allocator<std::string> >&) [(cmake) ???:-1]
0x703c33 : cmExportBuildFileGenerator::GenerateMainFile(std::ostream&) [(cmake) ???:-1]
0x707d5d : cmExportFileGenerator::GenerateImportFile() [(cmake) ???:-1]
0x54d205 : cmGlobalGenerator::Generate() [(cmake) ???:-1]
0x76abfe : cmGlobalUnixMakefileGenerator3::Generate() [(cmake) ???:-1]
0x53c38a : cmGlobalGenerator::DoGenerate() [(cmake) ???:-1]
0x609090 : cmake::Generate() [(cmake) ???:-1]
0x6093da : cmake::Run(std::vector<std::string, std::allocator<std::string> > const&, bool) [(cmake) ???:-1]
0x50eb76 : do_cmake(int, char const* const*) [(cmake) ???:-1]
0x5103ee : main [(cmake) ???:-1]
0x7fd391029a40 : __libc_start_main [(libc.so.6) ???:-1]
0x50d4fa : ??? [(???) ???:-1]


-- Generating done
-- Build files have been written to: /tmp/build
$