gcc先生のご意見:
nnn.c:8: 警告: implicit declaration of function 'strerror'
nnn.c:8: 警告: format '%s' expects type 'char *', but argument 3 has type 'int'

icc先生のご意見:
nnn.c(8): remark #981: operands are evaluated in unspecified order
printf("%d => %s\n", errno, strerror(errno));