compat: add strtok_r()

Windows does not have strtok_r (and while it does have an identical
strtok_s, but it is not obvious how to use it).  Grab an
implementation from glibc.

The svn-fe tool uses strtok_r to parse paths.

Acked-by: Johannes Sixt <j6t@kdbg.org>
Helped-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/git-compat-util.h b/git-compat-util.h
index 02a73ee..28d6b00 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -312,6 +312,11 @@
 extern uintmax_t gitstrtoumax(const char *, char **, int);
 #endif
 
+#ifdef NO_STRTOK_R
+#define strtok_r gitstrtok_r
+extern char *gitstrtok_r(char *s, const char *delim, char **save_ptr);
+#endif
+
 #ifdef NO_HSTRERROR
 #define hstrerror githstrerror
 extern const char *githstrerror(int herror);