[newlib-cygwin] Make gethostname, getdtablesize, mktemp, ualarm available in BSD, XOPEN_SOURCE >= 500.

[Corinna Vinschen]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=f70aad3de4d845f8b720010a2f8817db842d81e8

commit f70aad3de4d845f8b720010a2f8817db842d81e8
Author: Dionna Glaze <dionnaglaze@google.com>
Date:   Thu Jun 29 08:30:04 2017 +0200

    Make gethostname, getdtablesize, mktemp, ualarm available in BSD, XOPEN_SOURCE >= 500.

Diff:
---
 newlib/libc/include/sys/unistd.h | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/newlib/libc/include/sys/unistd.h b/newlib/libc/include/sys/unistd.h
index 84219ca..b60d340 100644
--- a/newlib/libc/include/sys/unistd.h
+++ b/newlib/libc/include/sys/unistd.h
@@ -259,9 +259,8 @@ int     _EXFUN(truncate, (const char *, off_t __length));
 #endif
 #endif
 
-#if defined(__CYGWIN__) || defined(__rtems__)
+#if defined(__BSD_VISIBLE) || (__XSI_VISIBLE >= 500)
 int	_EXFUN(getdtablesize, (void));
-int	_EXFUN(setdtablesize, (int));
 useconds_t _EXFUN(ualarm, (useconds_t __useconds, useconds_t __interval));
 #if !(defined  (_WINSOCK_H) || defined (_WINSOCKAPI_) || defined (__USE_W32_SOCKETS))
 /* winsock[2].h defines as __stdcall, and with int as 2nd arg */
@@ -270,6 +269,10 @@ useconds_t _EXFUN(ualarm, (useconds_t __useconds, useconds_t __interval));
 char *	_EXFUN(mktemp, (char *));
 #endif
 
+#if defined(__CYGWIN__) || defined(__rtems__)
+int	_EXFUN(setdtablesize, (int));
+#endif
+
 #if defined(__CYGWIN__) || defined(__SPU__) || defined(__rtems__)
 void    _EXFUN(sync, (void));
 #endif