Unbreak with clang6, and respect CXXFLAGS

Based on a diff from Matthew Martin.

security/steghide/Makefile

@@ -1,9 +1,9 @@
-# $OpenBSD: Makefile,v 1.14 2017/11/21 00:13:03 naddy Exp $
+# $OpenBSD: Makefile,v 1.15 2018/04/13 11:13:31 jca Exp $
 
 COMMENT =		software able to hide data in various kind of files
 
 DISTNAME =		steghide-0.5.1
-REVISION =		4
+REVISION =		5
 CATEGORIES =		security
 HOMEPAGE =		http://steghide.sf.net/
 
@@ -20,9 +20,14 @@ LIB_DEPENDS =		devel/gettext \
 			security/mhash \
 			graphics/jpeg
 WANTLIB =		c iconv intl jpeg m mhash mcrypt ${COMPILER_LIBCXX} z
-CONFIGURE_STYLE =	gnu
+CONFIGURE_STYLE =	autoconf
+AUTOCONF_VERSION =	2.57
 CONFIGURE_ENV =		CPPFLAGS="-I${LOCALBASE}/include" \
 			LDFLAGS="-L${LOCALBASE}/lib -liconv -lintl"
 
+.include <bsd.port.arch.mk>
+.if ${PROPERTIES:Mclang}
+CXXFLAGS +=		-std=c++03
+.endif
 
 .include <bsd.port.mk>

security/steghide/patches/patch-configure_in

@@ -0,0 +1,31 @@
+$OpenBSD: patch-configure_in,v 1.1 2018/04/13 11:13:31 jca Exp $
+
+Index: configure.in
+--- configure.in.orig
++++ configure.in
+@@ -15,6 +15,9 @@ AC_CHECK_FUNCS(strchr)
+ AM_GNU_GETTEXT
+ AM_CONDITIONAL(USE_INTLDIR, test "$nls_cv_use_gnu_gettext" = yes)
+ 
++dnl compiler warnings
++CXXFLAGS="-Wall $CXXFLAGS"
++
+ dnl check if debugging support is requested
+ AC_MSG_CHECKING([wether to enable debugging])
+ AC_ARG_ENABLE(debug,[  --enable-debug          enable debugging],
+@@ -22,14 +25,12 @@ AC_ARG_ENABLE(debug,[  --enable-debug          enable 
+ 	then
+ 		AC_MSG_RESULT([yes])
+ 		AC_DEFINE(DEBUG,1,[enable code used only for debugging])
+-		CXXFLAGS="-O2 -Wall -g"
++		CXXFLAGS="-g $CXXFLAGS"
+ 	else
+ 		AC_MSG_RESULT([no])
+-		CXXFLAGS="-O2 -Wall"
+ 	fi
+ 	,
+ 	AC_MSG_RESULT([no])
+-	CXXFLAGS="-O2 -Wall"
+ )
+ 
+ dnl check if randomness should be disabled