patch 9.0.0774: the libvterm code is outdated

Problem:    The libvterm code is outdated.
Solution:   Include libvterm changes from revision 802 to 817.  Revert some
            changes made for C89.
diff --git a/src/libvterm/t/30state_pen.test b/src/libvterm/t/30state_pen.test
index 915baec..92cf01d 100644
--- a/src/libvterm/t/30state_pen.test
+++ b/src/libvterm/t/30state_pen.test
@@ -112,3 +112,14 @@
 PUSH "\e[m\e[37;1m"
   ?pen bold = on
   ?pen foreground = idx(15)
+
+!Super/Subscript
+PUSH "\e[73m"
+  ?pen small = on
+  ?pen baseline = raise
+PUSH "\e[74m"
+  ?pen small = on
+  ?pen baseline = lower
+PUSH "\e[75m"
+  ?pen small = off
+  ?pen baseline = normal