patch 8.0.1240: MS-Windows: term_start() does not support environment

Problem:    MS-Windows: term_start() does not support environment.
Solution:   Implement the environment argument. (Yasuhiro Matsumoto, closes
            #2264)
diff --git a/src/proto/os_win32.pro b/src/proto/os_win32.pro
index 7e6953c..188a45b 100644
--- a/src/proto/os_win32.pro
+++ b/src/proto/os_win32.pro
@@ -67,4 +67,5 @@
 void set_alist_count(void);
 void fix_arg_enc(void);
 int mch_setenv(char *var, char *value, int x);
+void win32_build_env(dict_T *l, garray_T *gap);
 /* vim: set ft=c : */