Trying!

make: pkg-config: No such file or directory
make: pkg-config: No such file or directory
gcc -Wall -Wextra -Wno-unused-parameter -g -Og    -c -o input-example-libsystemd.o input-example-libsystemd.c
gcc   input-example-libsystemd.o sysfs-gpio.o   -o input-example-libsystemd
/usr/bin/ld: input-example-libsystemd.o: in function `main':
/home/debian/sysfs-gpio/input-example-libsystemd.c:24: undefined reference to `sd_event_default'
/usr/bin/ld: /home/debian/sysfs-gpio/input-example-libsystemd.c:29: undefined reference to `sd_event_add_io'
/usr/bin/ld: /home/debian/sysfs-gpio/input-example-libsystemd.c:35: undefined reference to `sd_event_loop'
/usr/bin/ld: input-example-libsystemd.o: in function `sd_event_unrefp':
/usr/include/systemd/sd-event.h:167: undefined reference to `sd_event_unref'
collect2: error: ld returned 1 exit status
make: *** [<builtin>: input-example-libsystemd] Error 1