patch 8.2.3666: libvterm is outdated

Problem:    Libvterm is outdated.
Solution:   Include patches from revision 769 to revision 789.
diff --git a/src/libvterm/vterm.pc.in b/src/libvterm/vterm.pc.in
index c64c72d..8d7e59a 100644
--- a/src/libvterm/vterm.pc.in
+++ b/src/libvterm/vterm.pc.in
@@ -1,6 +1,5 @@
-prefix=@PREFIX@
 libdir=@LIBDIR@
-includedir=${prefix}/include
+includedir=@INCDIR@
 
 Name: vterm
 Description: Abstract VT220/Xterm/ECMA-48 emulation library