How to compile NuSMV 2.6.0 from source - gcc

Question

I am trying to compile the software NuSMV 2.6.0 from source.
I clone the repo https://github.com/hklarner/NuSMV-a
I follow instructions in README.md:
cd NuSMV-2.6.0/NuSMV/
mkdir build
cd build
cmake ..
make
but I get the following error:
[ 16%] Building C object build-cudd/util/CMakeFiles/CUDD_UTIL_LIB.dir/getopt.c.o
[ 16%] Building C object build-cudd/util/CMakeFiles/CUDD_UTIL_LIB.dir/safe_mem.c.o
[ 16%] Building C object build-cudd/util/CMakeFiles/CUDD_UTIL_LIB.dir/strsav.c.o
[ 16%] Building C object build-cudd/util/CMakeFiles/CUDD_UTIL_LIB.dir/texpand.c.o
[ 17%] Building C object build-cudd/util/CMakeFiles/CUDD_UTIL_LIB.dir/ptime.c.o
[ 17%] Building C object build-cudd/util/CMakeFiles/CUDD_UTIL_LIB.dir/prtime.c.o
[ 17%] Building C object build-cudd/util/CMakeFiles/CUDD_UTIL_LIB.dir/pipefork.c.o
NuSMV-a/NuSMV-2.6.0/cudd-2.4.1.1/util/pipefork.c: In function ‘util_pipefork’:
NuSMV-a/NuSMV-2.6.0/cudd-2.4.1.1/util/pipefork.c:46:16: error: storage size of ‘status’ isn’t known
46 | union wait status;
| ^~~~~~
NuSMV-a/NuSMV-2.6.0/cudd-2.4.1.1/util/pipefork.c:53:12: warning: implicit declaration of function ‘pipe’ [-Wimplicit-function-declaration]
53 | (void) pipe(topipe);
| ^~~~
NuSMV-a/NuSMV-2.6.0/cudd-2.4.1.1/util/pipefork.c:59:20: warning: implicit declaration of function ‘vfork’ [-Wimplicit-function-declaration]
59 | if ((forkpid = vfork()) == 0) {
| ^~~~~
NuSMV-a/NuSMV-2.6.0/cudd-2.4.1.1/util/pipefork.c:62:9: warning: implicit declaration of function ‘dup2’ [-Wimplicit-function-declaration]
62 | (void) dup2(topipe[0], fileno(stdin));
| ^~~~
NuSMV-a/NuSMV-2.6.0/cudd-2.4.1.1/util/pipefork.c:65:9: warning: implicit declaration of function ‘close’; did you mean ‘pclose’? [-Wimplicit-function-declaration]
65 | (void) close(topipe[0]);
| ^~~~~
| pclose
NuSMV-a/NuSMV-2.6.0/cudd-2.4.1.1/util/pipefork.c:70:9: warning: implicit declaration of function ‘execvp’ [-Wimplicit-function-declaration]
70 | (void) execvp(argv[0], argv);
| ^~~~~~
NuSMV-a/NuSMV-2.6.0/cudd-2.4.1.1/util/pipefork.c:73:9: warning: implicit declaration of function ‘_exit’ [-Wimplicit-function-declaration]
73 | (void) _exit(1);
| ^~~~~
NuSMV-a/NuSMV-2.6.0/cudd-2.4.1.1/util/pipefork.c:73:9: warning: incompatible implicit declaration of built-in function ‘_exit’
make[2]: *** [build-cudd/util/CMakeFiles/CUDD_UTIL_LIB.dir/build.make:167: build-cudd/util/CMakeFiles/CUDD_UTIL_LIB.dir/pipefork.c.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:2174: build-cudd/util/CMakeFiles/CUDD_UTIL_LIB.dir/all] Error 2
I am on Ubuntu 20.04 LTS. I have no idea what I could do to fix this. It used to work.
Can anyone help?