cc -Wall -Werror -Wmissing-prototypes -I../posix_spawn -g -O2 
    -fsanitize=undefined -o cush -L../posix_spawn 
    cush.o shell-grammar.o list.o shell-ast.o termstate_management.o 
    utils.o signal_support.o -lspawn -ll -lreadline
/usr/bin/ld: termstate_management.o:/..../cs3214-cush/src/utils.h:11: 
    multiple definition of `job_list'; 
    cush.o:/..../cs3214-cush/src/utils.h:11: first defined here

/usr/bin/ld: utils.o:/..../cs3214-cush/src/utils.h:11: 
    multiple definition of `job_list'; 
    cush.o:/..../cs3214-cush/src/utils.h:11: first defined here

/usr/bin/ld: signal_support.o:/..../cs3214-cush/src/utils.h:11: 
    multiple definition of `job_list'; 
    cush.o:/..../cs3214-cush/src/utils.h:11: first defined here
collect2: error: ld returned 1 exit status
make: *** [Makefile:27: cush] Error 1