syscall \- indirect system call
.SH SYNOPSIS
.nf
-.BR "#define _GNU_SOURCE " " /* or _BSD_SOURCE or _SVID_SOURCE */"
+.BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */"
.B #include <unistd.h>
.BR "#include <sys/syscall.h> " "/* For SYS_xxx definitions */"