Move strtok_r implementation verbatim to helpers.c

Corresponding to flashrom svn r1853.

Signed-off-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
Acked-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
diff --git a/flash.h b/flash.h
index ff4b06b..81fd61b 100644
--- a/flash.h
+++ b/flash.h
@@ -255,6 +255,9 @@
 int min(int a, int b);
 char *strcat_realloc(char *dest, const char *src);
 void tolower_string(char *str);
+#ifdef __MINGW32__
+char* strtok_r(char *str, const char *delim, char **nextp);
+#endif
 
 /* flashrom.c */
 extern const char flashrom_version[];