clang can't link with gcc, so add the missing define in the clang case.

and it can't optimize malloc too much, or the undump magic fails.
(thanks to kettenis@ for the second part)

editors/emacs21/Makefile

@@ -1,4 +1,4 @@
-# $OpenBSD: Makefile,v 1.91 2016/11/20 15:14:19 jca Exp $
+# $OpenBSD: Makefile,v 1.92 2017/05/12 21:26:32 espie Exp $
 
 BROKEN-powerpc=		dumped executable fails with SIGABRT
 
@@ -86,3 +86,8 @@ post-install:
 	chmod -t ${PREFIX}/bin/emacs
 
 .include <bsd.port.mk>
+
+.if ${PROPERTIES:Mclang}
+CFLAGS +=	-fno-builtin-malloc
+.endif
+

editors/emacs21/patches/patch-src_s_openbsd_h

@@ -1,7 +1,8 @@
-$OpenBSD: patch-src_s_openbsd_h,v 1.2 2004/09/15 17:55:25 espie Exp $
---- src/s/openbsd.h.orig	Wed Mar 22 13:08:40 2000
-+++ src/s/openbsd.h	Mon Aug 30 12:04:49 2004
-@@ -9,3 +9,16 @@
+$OpenBSD: patch-src_s_openbsd_h,v 1.3 2017/05/12 21:26:32 espie Exp $
+Index: src/s/openbsd.h
+--- src/s/openbsd.h.orig
++++ src/s/openbsd.h
+@@ -9,3 +9,20 @@
  /*  David Mazieres <dm@reeducation-labor.lcs.mit.edu> says this
      is necessary.  Otherwise Emacs dumps core when run -nw.  */
  #undef LIBS_TERMCAP
@@ -18,3 +19,7 @@ $OpenBSD: patch-src_s_openbsd_h,v 1.2 2004/09/15 17:55:25 espie Exp $
 +#undef C_SWITCH_SYSTEM
 +#define C_SWITCH_SYSTEM -I/usr/X11R6/include -I/usr/local/include -L/usr/local/lib
 +#endif
++#ifdef __clang__
++#undef LIB_STANDARD
++#define LIB_STANDARD -lcompiler_rt -lc -lcompiler_rt /usr/lib/crtend.o
++#endif