patch 9.0.0774: the libvterm code is outdated

Problem:    The libvterm code is outdated.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/README b/src/libvterm/README
index 8e9341d..2641284 100644
--- a/src/libvterm/README
+++ b/src/libvterm/README
@@ -7,8 +7,11 @@
 	https://github.com/neovim/libvterm
 
 Modifications:
-- Add a .gitignore file.
-- Convert some code from C99 to C90.
+- revisions up to 817 have been included
+- Added a .gitignore file.
+- use TRUE and FALSE instead of true and false
+- use int or unsigned int instead of bool
+- Converted some code from C99 to C90.
 - Other changes to support embedding in Vim.
 
 To get the latest version of libvterm you need the "bzr" command and do: