It is quite simple to do in a standard makefile

GOVFLAGS= -lgov

# Library has been build, all objectfiles are left in build directory
timings: benchmark/timings.c $(LIBNAME)
    # compile benchmark/timings.c, link it with all objectfiles
    # and put executable in build directory
    $(CC) $(CFLAGS) $^ $(GOVFLAGS) -o timings

profiling:
    # Call makefile again with additional flag "-fprofile-arcs"
    # to generate the *gcda files while making the benchmark function
    make CFLAGS="$(CFLAGS) -fprofile-arcs" timings
    # run the "before" benchmark
    ./timings
    # remove static library and objectfiles. *gcda files stay, of course
    rm -f *.a *.o timings
    # Call makefile again with additional flag "-fbranch-probabilities"
    # to build the library with the actual optimizations.
    make CFLAGS="$(CFLAGS) -fbranch-probabilities"
        # snipped: part of benchmarking that builds and runs the "after"
    # benchmark

I was not able to find a method to call cmake recursively like make as shown above. I tried to do it by hand but I was not able to find a way to keep the *gcda files because I found no way to the same thing twice, as is needed for this method of profiling, and different targets compile in different sub-directories.

Another problem: its legacy code, so I have to take what is there, no changes in project structure (e.g. moving directories around etc.).

The build uses a separate directory for building (as in mkdir build && cd build && cmake .. -DOPTIONS=ARGS).

No modern cmake cmake_minimum_required(VERSION 3.10) available.

How can I call cmake from within CMakeLists.txt to translate the above makefile snippet into a working cmake-script?

Alternative solutions are welcome, too, of course, I am fully aware of the risk that it might be an XY problem!