textproc/topic: fix build with GCC-based architectures

Specifically specify signed char to fix build error on powerpc64.

PR:		237555
Approved by:	email@freebsd.hypermart.net (maintainer timeout), mat (mentor)
Differential Revision:	https://reviews.freebsd.org/D20285

textproc/topic/Makefile

@@ -11,8 +11,6 @@ COMMENT=	Topic markup parser
 
 LICENSE=	BSD2CLAUSE
 
-BROKEN_powerpc64=	Does not build: warning: comparison is always false due to limited range of data type
-
 PLIST_FILES=	bin/topic \
 		man/man1/topic.1.gz
 do-install:

textproc/topic/files/patch-linenoise.c

@@ -0,0 +1,11 @@
+--- linenoise.c.orig	2019-05-17 19:45:12 UTC
++++ linenoise.c
+@@ -749,7 +749,7 @@ static int linenoiseEdit(int stdin_fd, int stdout_fd, 
+ 
+     if (write(l.ofd,prompt,l.plen) == -1) return -1;
+     while(1) {
+-        char c;
++        signed char c;
+         int nread;
+         char seq[3];
+