patch 8.0.1832: cannot use :unlet for an environment variable
Problem: Cannot use :unlet for an environment variable.
Solution: Make it work. Use unsetenv() if available. (Ken Takata,
closes #2855)
diff --git a/src/proto/misc1.pro b/src/proto/misc1.pro
index 4e299e5..4b613e6 100644
--- a/src/proto/misc1.pro
+++ b/src/proto/misc1.pro
@@ -60,6 +60,7 @@
void expand_env_esc(char_u *srcp, char_u *dst, int dstlen, int esc, int one, char_u *startstr);
char_u *vim_getenv(char_u *name, int *mustfree);
void vim_setenv(char_u *name, char_u *val);
+void vim_unsetenv(char_u *name);
char_u *get_env_name(expand_T *xp, int idx);
char_u *get_users(expand_T *xp, int idx);
int match_user(char_u *name);