DetCommon Fixes, master branch (2021.03.17.)

This MR is trying to address 2 issues:

• The modification in DetCommon/cmake/PreConfig.cmake.in makes sure that the following wouldn't happen:

[bash][atlas]:build-test > cmake ../source/
-- The CXX compiler identification is Clang 12.0.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /opt/intel-clang/12.0.0/x86_64-centos7/bin/clang++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Found DetCommon: /cvmfs/atlas.cern.ch/repo/sw/software/22.0/DetCommon/22.0.28.1/InstallArea/x86_64-centos7-gcc8-opt/cmake/DetCommonConfig.cmake (version: 22.0.28.1)
-- Setting up LCG release "LCG_98python3" for platform: x86_64-centos7-gcc8-opt
-- Setting up LCG release using: /cvmfs/atlas.cern.ch/repo/sw/software/22.0/sw/lcg/releases/LCG_98python3/LCG_externals_x86_64-centos7-gcc8-opt.txt
-- Setting ATLAS specific build flags
-- Configuring done
CMake Error at CMakeLists.txt:10 (add_executable):
  Target "testExe" links to target "Threads::Threads" but the target was not
  found.  Perhaps a find_package() call is missing for an IMPORTED target, or
  an ALIAS target is missing?


CMake Error at CMakeLists.txt:10 (add_executable):
  Target "testExe" links to target "Threads::Threads" but the target was not
  found.  Perhaps a find_package() call is missing for an IMPORTED target, or
  an ALIAS target is missing?


-- Generating done
CMake Generate step failed.  Build files cannot be regenerated correctly.
[bash][atlas]:build-test >

• The change in TrigConfData/CMakeLists.txt is there to make it easier to compile the L1Calo and CTP code at Point-1. As discussed in ATLINFR-3977.

Pinging @fwinkl and @rhauser.