editors/elvis with clang

Hi,

By declaring both UP and BC as extern it's possible to compile editors/elvis
with clang.

OK?

Index: patches/patch-guitcap_c
===================================================================
RCS file: patches/patch-guitcap_c
diff -N patches/patch-guitcap_c
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ patches/patch-guitcap_c 26 May 2017 12:34:51 -0000
@@ -0,0 +1,26 @@
+$OpenBSD$
+
+Index: guitcap.c
+--- guitcap.c.orig
++++ guitcap.c
+@@ -15,11 +15,7 @@
+ * variable. Others (particularly ncurses) forbid it. The nice ones
+ * supply one if you don't, so they'll work either way.
+ */
+-#ifdef NEED_BC
+- char *BC; /* :bc=: move cursor left */
+-#else
+ extern char *BC; /* :bc=: move cursor left */
+-