[newlib-cygwin] Add man page entry for strnstr.c.

[newlib-cygwin] Add man page entry for strnstr.c.

[Corinna Vinschen]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=42885ea4b8bfece01cac0a4a4030ff4341454353

commit 42885ea4b8bfece01cac0a4a4030ff4341454353
Author: Sichen Zhao <1473996754@qq.com>
Date:   Wed Aug 30 11:03:57 2017 +0800

    Add man page entry for strnstr.c.

Diff:
---
 newlib/libc/string/strings.tex |  4 ++++
 newlib/libc/string/strnstr.c   | 39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/newlib/libc/string/strings.tex b/newlib/libc/string/strings.tex
index c619886..6aec5fe 100644
--- a/newlib/libc/string/strings.tex
+++ b/newlib/libc/string/strings.tex
@@ -40,6 +40,7 @@ managing areas of memory.  The corresponding declarations are in
 * strncat::     Concatenate strings
 * strncmp::     Character string compare
 * strncpy::     Counted copy string
+* strnstr::     Find string segment
 * strnlen::     Character string length
 * strpbrk::     Find chars in string
 * strrchr::     Reverse search for character in string
@@ -159,6 +160,9 @@ managing areas of memory.  The corresponding declarations are in
 @include string/strncpy.def
 
 @page
+@include string/strnstr.def
+
+@page
 @include string/strnlen.def
 
 @page
diff --git a/newlib/libc/string/strnstr.c b/newlib/libc/string/strnstr.c
index 05d86ee..fcceebc 100644
--- a/newlib/libc/string/strnstr.c
+++ b/newlib/libc/string/strnstr.c
@@ -1,3 +1,42 @@
+/*
+FUNCTION
+	<<strnstr>>---find string segment
+
+INDEX
+	strnstr
+
+ANSI_SYNOPSIS
+	#include <string.h>
+	size_t strnstr(const char *<[s1]>, const char *<[s2]>, size_t <[n]>);
+
+TRAD_SYNOPSIS
+	#include <string.h>
+	size_t strnstr(<[s1]>, <[s2]>, <[n]>)
+	char *<[s1]>;
+        char *<[s2]>;
+	size_t <[n]>;
+
+DESCRIPTION
+	Locates the first occurrence in the string pointed to by <[s1]> of
+	the sequence of limited to the <[n]> characters in the string
+        pointed to by <[s2]>
+
+RETURNS
+	Returns a pointer to the located string segment, or a null
+	pointer if the string <[s2]> is not found. If <[s2]> points to
+	a string with zero length, <[s1]> is returned.
+
+
+PORTABILITY
+<<strnstr>> is ANSI C.
+
+<<strnstr>> requires no supporting OS subroutines.
+
+QUICKREF
+	strnstr ansi pure
+
+*/
+
 #undef __STRICT_ANSI__
 #include <_ansi.h>
 #include <string.h>