configure: pipe2 and accept4 are NOT Linux-specific

While both system calls originate on Linux, they are part of POSIX.next
and implemented by FreeBSD 10.0 and other OSes.

configure.ac

@@ -590,7 +590,7 @@ dnl Check for system libs needed
 need_libc=false
 
 dnl Check for usual libc functions
-AC_CHECK_FUNCS([daemon fcntl flock fstatvfs fork getenv getpwuid_r isatty lstat memalign mkostemp mmap open_memstream openat pread posix_fadvise posix_madvise posix_memalign setlocale stricmp strnicmp strptime tdestroy uselocale])
+AC_CHECK_FUNCS([accept4 daemon fcntl flock fstatvfs fork getenv getpwuid_r isatty lstat memalign mkostemp mmap open_memstream openat pipe2 pread posix_fadvise posix_madvise posix_memalign setlocale stricmp strnicmp strptime tdestroy uselocale])
 AC_REPLACE_FUNCS([aligned_alloc atof atoll dirfd fdopendir ffsll flockfile fsync getdelim getpid lldiv memrchr nrand48 poll recvmsg rewind sendmsg setenv strcasecmp strcasestr strdup strlcpy strndup strnlen strnstr strsep strtof strtok_r strtoll swab tfind timegm timespec_get strverscmp pathconf])
 AC_REPLACE_FUNCS([gettimeofday])
 AC_CHECK_FUNC(fdatasync,,
@@ -622,7 +622,7 @@ AC_FUNC_STRCOLL
 dnl Check for non-standard system calls
 case "$SYS" in
   "linux")
-    AC_CHECK_FUNCS([accept4 pipe2 eventfd vmsplice sched_getaffinity recvmmsg memfd_create])
+    AC_CHECK_FUNCS([eventfd vmsplice sched_getaffinity recvmmsg memfd_create])
     ;;
   "mingw32")
     AC_CHECK_FUNCS([_lock_file])