archivers/zstd: workaround for missing LESSOPEN support in zstdless

The `zstdless` script, which is part of the zstd package, relies on the
LESSOPEN mechanism, which was removed from OpenBSD over a year ago. As a
result, `zstdless` is currently broken. Work around this by replacing
`zstdless` with a script using `zstdcat` and `less`.

Issue reported and workaround suggested by Tom Szilagyi <tom DOT
szilagyi AT altmail DOT se>.

archivers/zstd/Makefile

@@ -1,6 +1,7 @@
 COMMENT =		zstandard fast real-time compression algorithm
 
 V =			1.5.7
+REVISION =		0
 DISTNAME =		zstd-${V}
 
 SHARED_LIBS =		zstd	7.0	# 1.5.7

archivers/zstd/patches/patch-programs_zstdless

@@ -0,0 +1,13 @@
+Index: programs/zstdless
+--- programs/zstdless.orig
++++ programs/zstdless
+@@ -1,8 +1,3 @@
+ #!/bin/sh
+ 
+-zstd=${ZSTD:-zstd}
+-
+-# TODO: Address quirks and bugs tied to old versions of less, provide a mechanism to pass flags directly to zstd
+-
+-export LESSOPEN="|-${zstd} -cdfq %s"
+-exec less "$@"
++zstdcat "$@" | less