patch 9.0.0774: the libvterm code is outdated

Problem:    The libvterm code is outdated.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/run-test.pl b/src/libvterm/t/run-test.pl
index 7d5cc7b..3440465 100644
--- a/src/libvterm/t/run-test.pl
+++ b/src/libvterm/t/run-test.pl
@@ -124,7 +124,7 @@
       elsif( $line =~ m/^putglyph (\S+) (.*)$/ ) {
          $line = "putglyph " . join( ",", map sprintf("%x", $_), eval($1) ) . " $2";
       }
-      elsif( $line =~ m/^(?:movecursor|scrollrect|moverect|erase|damage|sb_pushline|sb_popline|settermprop|setmousefunc|selection-query) / ) {
+      elsif( $line =~ m/^(?:movecursor|scrollrect|moverect|erase|damage|sb_pushline|sb_popline|sb_clear|settermprop|setmousefunc|selection-query) ?/ ) {
          # no conversion
       }
       elsif( $line =~ m/^(selection-set) (.*?) (\[?)(.*?)(\]?)$/ ) {