[Windows] Building uncrustify_vendor: No CMAKE_CXX_COMPILER could be found

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I'm building the ROS 2 packages from source following the Windows source tutorial, but I'm getting stuck when I try to build the uncrustify_vendor package. CMake reports that C/C++ compilers cannot be found. Following is the traceback I see:

C:\dev\ros2_rolling>colcon build --merge-install --packages-select uncrustify_vendor --event-handlers console_direct+
Starting >>> uncrustify_vendor
-- Selecting Windows SDK version 10.0.19041.0 to target Windows 10.0.19044.
-- Found ament_cmake: 1.2.0 (C:/dev/ros2_rolling/install/share/ament_cmake/cmake)
-- Configuring done
-- Generating done
-- Build files have been written to: C:/dev/ros2_rolling/build/uncrustify_vendor
Microsoft (R) Build Engine version 16.11.2+f32259642 for .NET Framework
Copyright (C) Microsoft Corporation. All rights reserved.

  Checking Build System
  Performing configure step for 'uncrustify-45b836cff040594994d364ad6fd3f04adc890a26'
  -- Selecting Windows SDK version 10.0.19041.0 to target Windows 10.0.19044.
  -- The C compiler identification is unknown
  -- The CXX compiler identification is unknown
  CMake Error at CMakeLists.txt:3 (project):
    No CMAKE_C_COMPILER could be found.



  CMake Error at CMakeLists.txt:3 (project):
    No CMAKE_CXX_COMPILER could be found.



  -- Configuring incomplete, errors occurred!
  See also "C:/dev/ros2_rolling/build/uncrustify_vendor/uncrustify-45b836cff040594994d364ad6fd3f04adc890a26-prefix/src/uncrustify-45b836cff040594994d364ad6fd3f04adc890a26-build/CMakeFiles/CMakeOutput.log".
  See also "C:/dev/ros2_rolling/build/uncrustify_vendor/uncrustify-45b836cff040594994d364ad6fd3f04adc890a26-prefix/src/uncrustify-45b836cff040594994d364ad6fd3f04adc890a26-build/CMakeFiles/CMakeError.log".
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Microsoft\VC\v160\Microsoft.CppCommon.targets(241,5): error MSB8066: Custom build for 'C:\dev\ros2_rolling\build\uncrustify_vendor\CMakeFiles\d177f57d11cdf441cb98984155862ddc\uncrustify-45b836cff040594994d364ad6fd3f04adc890a26-configure.rule;C:\dev\ros2_rolling\build\uncrustify_vendor\CMakeFiles\d177f57d11cdf441cb98984155862ddc\uncrustify-45b836cff040594994d364ad6fd3f04adc890a26-build.rule;C:\dev\ros2_rolling\build\uncrustify_vendor\CMakeFiles\d177f57d11cdf441cb98984155862ddc\uncrustify-45b836cff040594994d364ad6fd3f04adc890a26-install.rule;C:\dev\ros2_rolling\build\uncrustify_vendor\CMakeFiles\1f61a89c37b27fe4d1c79f10968d9730\uncrustify-45b836cff040594994d364ad6fd3f04adc890a26-complete.rule;C:\dev\ros2_rolling\build\uncrustify_vendor\CMakeFiles\6aaed628ba48b5d83eef28c741094c56\uncrustify-45b836cff040594994d364ad6fd3f04adc890a26.rule;C:\dev\ros2_rolling\src\ament\uncrustify_vendor\CMakeLists.txt' exited with code 1. [C:\dev\ros2_rolling\build\uncrustify_vendor\uncrustify-45b836cff040594994d364ad6fd3f04adc890a26.vcxproj]
Failed   <<< uncrustify_vendor [6.84s, exited with code 1]

Summary: 0 packages finished [10.4s]
  1 package failed: uncrustify_vendor

Any clues what could be going wrong here? I've done:

1. Simple sanity checks in building test programs with cmake and Visual C++ 2019.
2. Read (and tried suggestions) some stackoverflow posts about similar reports.

3. Read some ROS answers posts about similar reports.

   One commenter suggested replacing the CMakeLists.txt file in uncrustify_vendor with that of an older distribution (Foxy) - this worked, but I'm not sure why it did and whether that reflects a bug in the master branch or just a regression in my setup. Should I report this as an issue on Github?

Any help would be much appreciated!