/in/foo.c: In function 'main':
/in/foo.c:54:9: warning: implicit declaration of function 'strrev' [-Wimplicit-function-declaration]
         strrev(b[0]);
         ^~~~~~
/tmp/ccblITzD.o: In function `main':
foo.c:(.text.startup+0x7e): undefined reference to `strrev'
foo.c:(.text.startup+0xa3): undefined reference to `strrev'
foo.c:(.text.startup+0xc8): undefined reference to `strrev'
collect2: error: ld returned 1 exit status