Provide WORKING_DIRECTORY when use execute_process in CMake

[ivan-ushakov]

Release v1.4.1 has following code in CMake:

if(UA_ENABLE_MQTT)
    if(NOT EXISTS "${UA_FILE_MQTT}")
        message(STATUS "Submodule update")
        execute_process(COMMAND ${GIT_EXECUTABLE} submodule update --init --recursive
                        RESULT_VARIABLE GIT_SUBMOD_RESULT)
        if(NOT GIT_SUBMOD_RESULT EQUAL "0")
            message(FATAL_ERROR "git submodule update --init --recursive failed with ${GIT_SUBMOD_RESULT}")
        endif()
    endif()
    include_directories("${PROJECT_SOURCE_DIR}/deps/mqtt-c/include")
endif()

It is better to provide WORKING_DIRECTORY for execute_process(). Otherwise it leads to error like this if you use FetchContent_Declare:

#21 31.97 -- Submodule update
#21 31.98 fatal: not a git repository (or any of the parent directories): .git
#21 31.98 CMake Error at build/_deps/open62541-src/CMakeLists.txt:376 (message):
#21 31.98   git submodule update --init --recursive failed with 128

[juwalter]

it would be great to have this, since we include open62541 into our cmake-based project using

FetchContent_Declare(
  open62541
  GIT_REPOSITORY https://github.com/open62541/open62541.git
  GIT_TAG v1.4.1
  GIT_SHALLOW TRUE
  SYSTEM
  #PATCH_COMMAND git apply ${CMAKE_SOURCE_DIR}/cmake/my_open62541.patch
)

set(UA_LOGLEVEL 100 CACHE STRING "Minimal level at which logs shall be reported (100=TRACE, 200=DEBUG, 300=INFO, 400=WARNING, 500=ERROR, 600=FATAL)" FORCE)
# ... more

FetchContent_MakeAvailable(open62541)

and right now, this automatically works in a locally checked out project (since we have a .git folder), but during build in e.g. Docker we need to do a work-around git init to satisfy this (note: FetchContent_Declare takes care of cloning all submodules recursively)

fyi: "offending" code is at https://github.com/open62541/open62541/blob/master/CMakeLists.txt#L367

btw- UA_FILE_MQTT also does not seem to be declared anywhere? (checked a few lines above)