build yaml-cpp lib with -m32 (32-bit) - on linux /w gcc or llvm

subject pretty much says it all:

• I downloaded yaml-cpp version 0.6.3.
• I need to compile on linux x86_64, target linux x86_32 (build on 64 bit, use result on 32-bit)
• I have been trying to add a new "YAML_BUILD_32BIT" option - similar to the existing YAML_BUILD_SHARED_LIBS option.

When I detect YAML_BUILD_32BIT is set: I try to add "-m32" to a bunch of cmake variables. My problem is that this list of variables seems endless or not well defined.

• "yaml_cxx_flags" are passed to the compile and link steps for the yaml-cpp library code...but not to build the google 'mock' code. Similarly, I found other variables that I can also set, so that google-mock is compiled with -m32 as well...but then the yaml-cpp mock tests do not see the flag...and so on and so on.

I think I am missing something very fundamental. I expect that there will be a single variable I need to update...maybe 2 or 3. I don't expect to keep finding more and more.

--

Adding more specifics:

To CMakeLists.txt:

• added line (immediately after the similar line which creates the YAML_BUILD_SHARED_LIBS flag)

option(YAML_BUILD_32BIT "Build with '-m32'" OFF)

• then a bit later (immediately after the YAML_BUILD_SHARED_LIBS if/else):

   if(YAML_BUILD_32BIT)
     # seem to need this one for the shared lib link of yaml-cpp lib
     #  CXX_FLAGS passed to both compile and link
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -m32")
     # seem to need this one, to get flag passed to gmock build
     set(FLAG_TESTED "${FLAG_TESTED} -m32")
     # this one passed to compile and link of testcase
     set(yaml_cxx_flags "${yaml_cxx_flags} -m32")
   endif()

• and made "FLAG_TESTED" addive, on immediately following line:

    set(FLAG_TESTED "-Wextra -Wshadow -Weffc++ -pedantic -pedantic-errors ${FLAG_TESTED}")

Given the above, then configuring with:

  # using cmake/3.19.3
  cmake -G "Unix Makefiles" -DYAML_BUILD_SHARED_LIBS=ON -DYAML_BUILD_32BIT=ON"

... and then building with 'make VERBOSE=1', I see that 'gmock-all.cc.o' did not receive the -m32 flag. (gmock-all.cc.o is only the first such file in my log..there are others.) If I remove other of the lines in my CMakeLists.txt which attempted to add flags - then other compile commands or other link commands don't see -m32 and will fail.

As I said: I think there is something fundamental that I have misunderstood. I suspect that it is much easier to configure a 32-bit build than I am making it.