net-im/centerim{,-devel}: Fix build with Clang 6

In file included from rsshook.cc:32:
../../src/icqface.h:248:50: error: cannot combine with previous 'bool' declaration specifier
        bool findresults(const imsearchparams &sp, bool auto = false);
                                                        ^

... and more if one gets past this

http://beefy12.nyi.freebsd.org/data/head-amd64-default/p479076_s338486/logs/errors/centerim-4.22.10_5.log
http://beefy12.nyi.freebsd.org/data/head-amd64-default/p479076_s338486/logs/errors/centerim-devel-4.22.10.11_7.log

PR:		230904
Approved by:	frank@altpeter.de (maintainer timeout, 2 weeks)

net-im/centerim-devel/Makefile

@@ -18,6 +18,7 @@ LICENSE_FILE=	${WRKSRC}/COPYING
 LIB_DEPENDS=	libcurl.so:ftp/curl
 
 USES=		iconv gmake ncurses perl5 pkgconfig python:2.7,run shebangfix ssl
+USE_CXXSTD=	gnu++98
 USE_PERL5=	run
 GNU_CONFIGURE=	yes
 CONFIGURE_ARGS=	--with-ssl --with-openssl

net-im/centerim/Makefile

@@ -19,6 +19,7 @@ LIB_DEPENDS=	libassuan.so:security/libassuan \
 		libgpg-error.so:security/libgpg-error
 
 USES=		iconv gmake ncurses pkgconfig python shebangfix ssl
+USE_CXXSTD=	gnu++98
 GNU_CONFIGURE=	yes
 CPPFLAGS+=	-I${LOCALBASE}/include
 CXXFLAGS+=	-I${LOCALBASE}/include