patch 8.0.0741: cannot build with HPUX

Problem:    Cannot build with HPUX.
Solution:   Rename envbuf_TERM to envbuf_Term. (John Marriott)
diff --git a/src/os_unix.c b/src/os_unix.c
index 9869d30..ad70465 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -4059,7 +4059,7 @@
 # ifdef HAVE_SETENV
     char	envbuf[50];
 # else
-    static char	envbuf_TERM[30];
+    static char	envbuf_Term[30];
     static char	envbuf_Rows[20];
     static char	envbuf_Lines[20];
     static char	envbuf_Columns[20];