cc -O2 -pipe  -pthread  -Wall -Wextra -Werror=implicit-function-declaration fmtmsg/fmtmsg.c -o fmtmsg/fmtmsg -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm -lpthread 
fmtmsg/fmtmsg.c:4:10: fatal error: 'fmtmsg.h' file not found
    4 | #include <fmtmsg.h>
      |          ^~~~~~~~~~
1 error generated.