ITKModuleExternal cmake include missing

I just built ITK from source with `cmake ..`and `make` followed by `sudo make install`. I hoped to pull all ITK dependencies this way. It appears not:

```console
mini-me@virtucon ~/h/c/i/build (main)> cmake ..
-- The C compiler identification is GNU 11.4.0
-- The CXX compiler identification is GNU 11.4.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
CMake Warning (dev) at /usr/share/cmake-3.22/Modules/CTest.cmake:50 (option):
Policy CMP0077 is not set: option() honors normal variables. Run "cmake
--help-policy CMP0077" for policy details. Use the cmake_policy command to
set the policy and suppress this warning.

For compatibility with older versions of CMake, option is clearing the
normal variable 'BUILD_TESTING'.
Call Stack (most recent call first):
build/_deps/libcbor-src/CMakeLists.txt:4 (include)
This warning is for project developers. Use -Wno-dev to suppress it.

-- Looking for sys/types.h
-- Looking for sys/types.h - found
-- Looking for stdint.h
-- Looking for stdint.h - found
-- Looking for stddef.h
-- Looking for stddef.h - found
-- Check size of size_t
-- Check size of size_t - done
-- LTO is enabled
-- Looking for ldexp
-- Looking for ldexp - found
-- Performing Test COMPILER_HAS_HIDDEN_VISIBILITY
-- Performing Test COMPILER_HAS_HIDDEN_VISIBILITY - Success
-- Performing Test COMPILER_HAS_HIDDEN_INLINE_VISIBILITY
-- Performing Test COMPILER_HAS_HIDDEN_INLINE_VISIBILITY - Success
-- Performing Test COMPILER_HAS_DEPRECATED_ATTR
-- Performing Test COMPILER_HAS_DEPRECATED_ATTR - Success
CMake Error at CMakeLists.txt:126 (include):
include could not find requested file:

ITKModuleExternal

CMake Error at CMakeLists.txt:130 (itk_module_target_label):
Unknown CMake command "itk_module_target_label".

-- Configuring incomplete, errors occurred!
See also "/home/mini-me/home/cellar/itk-wasm/build/CMakeFiles/CMakeOutput.log".
```

This is likely a problem in ITK itself, but as it impacts itk-wasm, it seems not incorrect to open an issue here.