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: in function `termstate_save':
/..../cs3214-cush/src/termstate_management.c:48: 
    undefined reference to `saved_tty_state'
/usr/bin/ld: termstate_management.o: in function 
    `termstate_give_terminal_back_to_shell':
/..../cs3214-cush/src/termstate_management.c:107: 
    undefined reference to `saved_tty_state'
/usr/bin/ld: termstate_management.o: in function `termstate_save':
/..../cs3214-cush/src/termstate_management.c:48: 
    undefined reference to `saved_tty_state'
collect2: error: ld returned 1 exit status
make: *** [Makefile:27: cush] Error 1