Fix "error: implicit declaration of function 'makeTetrix'" and another
problem fixed by the same upstream commit.
https://gitlab.com/graphviz/graphviz/-/commit/b4947d67a4ebd48ca0105d44f92e47f044e51600
--- cmd/lefty/dot2l/dotlex.c.orig	2016-08-09 16:02:09.000000000 -0500
+++ cmd/lefty/dot2l/dotlex.c	2020-08-27 14:45:45.000000000 -0500
@@ -252,7 +252,7 @@
     char *q;
 
     q = lexbuf;
-    if (p == '\0')
+    if (!p || *p == '\0')
         return NULL;
     while (isalnum (*p) || (*p == '_') || (!isascii (*p)))
         *q++ = *p++;
--- cmd/tools/gvgen.c.orig	2016-11-22 23:43:56.000000000 -0600
+++ cmd/tools/gvgen.c	2020-08-27 14:45:45.000000000 -0500
@@ -458,6 +458,8 @@
 	fprintf(opts.outfile, "}\ngraph {\n");
 }
 
+extern void makeTetrix(int depth, edgefn ef);
+
 int main(int argc, char *argv[])
 {
     GraphType graphType;